Which new gun to go for?

Couldn't figure out whether to put this in New Recruits or The Arsenal, so here it is.
While I would just make them myself and see what I like, I'm a little short on money and time at the moment.
Since I've been on hiatus I haven't really been keeping up with the new guns. After coming back I do want to make some but I honestly can't choose and I'd simply like recommendations on which to choose from people more knowledgeable than myself; after asking around some of the guns I initially wanted actually seem to be considered "bad" or "sub-par" by the majority of people I asked, so here I am for a final opinion.
Skip this if you want, it's just my thoughts if you care to know what I'm looking at, at the moment: initially I wanted Riftlocker and Winter Grave, and although I still have my sights set on obtaining Winter Grave, I've heard over and over again that Riftlocker is not that great. Besides those two, I'd like Arcana simply to replace my Polaris and Drivers as a basic Elemental gun; the fact that it makes a good Lockdown gun also somewhat appeals to me though that's irrelevant as I'm looking at this solely from a PvE-perspective. Phantamos I wanted simply because I love all the Shadow weapons though I can't see myself using it over Umbra Driver. Wildfire I find to be Polaris but slightly less useful (I actually like that Polaris shocks enemies because it lets me freely slay Gun Puppies and Howlitzers with no risk among other things besides being a DPS machine against a shocked enemy), and really the only place I can see myself using it over Polaris is Ghosts in the Machine. I'm not getting Gilded Griffon: I hated Antiguas before the update, and I recognize that they are actually good now, but I still hate them and Gilded Griffon lives in Callahan's shadow in my opinion (and I can't even get it for the sake of speedrunning areas, as Carbine works best in Piercing areas, Sentenza works best in Elemental areas, and Argent Peacemaker works best in Shadow areas, and I have all three of those). I'm quite interested in Permafroster due to its Shadow damage as well as Freeze being useful; the same reasons I want Winter Grave. I can't even see any area where Grim Repeater is useful (if you tell me Jelly King, I'm going to tell you Dark Retribution and move on).
So basically my options as it stands are Winter Grave, Arcana, and Permafroster, but I'd like a second opinion on this. May be worth noting that I do have every pre-update gun besides Overcharged Mixmaster, so I'm mostly looking for a gun that is fun and interesting while still retaining usability and filling a role that the previous guns may not have (which is why Winter Grave interests me so much). Sorry for somewhat medium-long post I think? I just would like a solid opinion on this.

I don't really like Winter Grave, the freeze keeps enemies from being pushed back and getting hit even more. Callahan/Iron Slug will usually be more effective since their charges can get more hits in. The only time I might use it would be attacking enemies that are immobile anyway like polyps.
Arcana is nice though, I use that instead of AP when I want the slight knockback over firing more quickly.
Riftlocker doesn't seem to useful to me. Could use it for fun against devilites but like you said, Callahan is better against more enemies and since you're already comparing guns to bombs, I'm going to tell you Dark Briar Barrage and move on.
The only place I really use Grim Repeater is the lichen lair areas. Don't need it for RJP, and Blitz is good enough in OCH.
I don't use the pulsars much anymore so I won't comment on them. Permafroster would be good against polyps, I guess.

https://gyazo.com/daa21a5c949e908ee7172d917b2bd9bf
I'm now interested in what happened before here. Who was talking, what was he asking you to make?
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Are the guns shown in the image all of the 5* guns you own, or are there more?

I can't easily tell from your post exactly what guns you have and what you're looking for in a gun. You make some statements such as "Carbine works best in Piercing areas" that don't make much sense to me. (Monsters dealing piercing, or monsters vulnerable to piercing? Neither makes sense to me. Better than in other areas, or better than other guns? Neither makes sense to me.) So I'll just make my usual remarks:
There are now so many guns, including most styles in most damage types, that you can pick the styles you want and then pick almost any combination of damage types that you want. So focus on style.
* Blasters and antiguas are not terrible, but they are not great, and they are extremely boring. I don't recommend Arcana, Riftlocker, Obsidian, etc.
* Pulsars are fascinating and useful when used well --- for clever crowd control, not damage. But you want to replace yours?
* Alchemers are quite powerful (once you master the ricochets) and quite fun. But you want to replace yours? Trying out new guns is fun, but don't be surprised if you come back to them. Magnuses are also quite powerful and fun. Autoguns are powerful but somewhat tedious.
* You don't seem to be considering the other styles, such as catalyzers and tortofists. Okay.

Sorry that I wasn't informative enough in my OP, I'll try answering some of those questions in this one, but first, thanks Fehzor for pointing out OCH and Dreams and Nightmares for being great places for GR; I thought about C42 for awhile but eventually decided I'd be better off with GF and Umbra than GR in any situation there, but I hadn't thought of those two-- definitely considering GR now.
Here's all the guns I currently have: http://imgur.com/a/Tc6Ec
Most notably, I have all the pre-update guns besides Overcharged Mixmaster and three of the Tortofists (I honestly don't see the point in making them, but I could if I really wanted to). Besides that, I have the 3* version of every new gun except for Grim Repeater (overlooked it initially, I'll make it soon).
When I mentioned "Carbine works best in Piercing areas", I was specifically referring to using Gilded Griffon as a gun for speedrunning areas; and by Piercing areas, I meant enemies that deal Piercing damage. So in conclusion, when speedrunning areas with Slimes and Wolvers, Carbine is best due to Slimes resisting Gilded Griffon, Wolvers resisting Argent Peacemaker, and Sentenza not putting its effect to use. When speedrunning Elemental areas, Sentenza/Carbine is best due to Gremlins resisting Argent Peacemaker, Constructs resisting Gilded Griffon, and Sentenza being able to use its effect to its full extent. In areas with Undead and Fiends, I would honestly prefer Argent Peacemaker to Gilded Griffon, though I suppose this one could be seen as a tie; initially I hadn't thought about that, but I was just pointing out that one reason for making Gilded Griffon (speedrunning) was not a valid reason in my mind. Hope that clears things up.
As for considering the other guns, I have most of the other guns, so I know their strengths and weaknesses well enough (at least I hope so!), which is why I wasn't considering them; probably should have put that at the start of the OP.
Sorry I can't really be more informative, I'm trying my best here! Dibsville whines pathetically.

Oh, I see. Then my earlier post is mostly useless.
My answer would be the new Iron Slug (which you already have), the new Callahan (which you already have), and maybe Grim Repeater. You might also try the fire pulsar for knockback. Like Flowchart I'm not a big fan of Winter Grave, because freeze hurts the knockback and hence the damage. If only it dealt poison or stun or something...
The other new guns are all damage variations on guns that you already know. So I don't see much point in getting them, unless a great gun (Blitz Needle) is suddenly available in a new damage type (Grim Repeater).
You seem to be putting a lot of thought into the antiguas. But you already know exactly what they'll do. And if you're like me then you find that gun type really tedious. But to each his own. Cheers.

Personally I like WG's freeze, because it allows for more interesting dynamics with the attacks end-range. A slug/callahan will push the monster, while the WG may add in another damaging attack if it freezes on the first.
Slug/callahan are definitely more lethal with close/mid-range monsters facing towards the charge.
WG is less lethal for close/mid-range, but is significantly more lethal at max range, with facing direction being less important (better for non-solo).
Grim repeater is excellent against all manner of gremlin, slime and construct. This happens to include Seerus, compound 42 and many enemies on dreams and nightmares.
Winter grave is the other best choice that stands out to me. Many will tell you not to bother with it since it doesn't knock them back all the way, but the ice makes it better in a different way that you've probably seen before- the freeze + charge again way. This makes it quite possibly the single best weapon to fight tortodrones with, and it's plausible that more things will come out in the future for it to hard-counter in this way.
Arcana doesn't really stand out much but is still fairly useful as just "an elemental gun". I do get a lot of use out of mine, though I'd honestly rather you craft it later since it doesn't expand your capabilities nearly as much as just using valiance.
Permafroster I'm really not so impressed with. It does freeze and then break its own freeze, which is good because it means enemies get hit twice and knocked back, but it can also be a tremendous safety hazard and in general has been a lot more trouble than it's worth. It's fun to use since it's a shadow polaris and all that, but I'd get it later than sooner.