I currently have Valiance and Plague Needle. I would like to start working on a different gun. What do you suggest would help me and why?
I was looking at I think the Polaris or Supernova. Not sure what the difference between them is. What else is out there for a really good gun? Thanks for the help!
Pick the Polaris if you're choosing between Supernova and it.
Umbra and Biohazard are both decent picks, the Sentenza is terrible. The only thing the Sentenza is good against, will dodge your shots like crazy, not to mention it's terribly weak shots to the things it's good against. Even in PVP I felt that the Sentenza isn't that great, it's a peashooter. The Biohazard is probably the best gun you can get for Royal Jelly Palace, it's charge is not dumb to use at all, it does a load of damage, it's a controlled explosion unlike the Polaris and Supernova, has a good chance of poisoning when using the explosion and it's excellent for kiting. (ex. running around a mob of jelly while tagging them with the charged shots, then shooting it for crazy damage on the clumped jigglers.) The Umbra is pretty good against gremlins because of the quick bullets, and the ricochet helps when they happen to dodge.
How do you have two 5-star guns before learning the difference between two lines of one of the most popular gun families? As long as you have a weapon you can use well with good direct damage in each of two damage types, you'll be in good shape weapon-wise. A lot of recommendations depend a lot on whether you use 2 weapon slots or more, and whether you intend to use just guns or combine them with swords and/or bombs. Giving more information about what you intend to do will help people give recommendations that are relevant to you.
One thing that does not depend much on those variables, though, is recommending ANY Elemental gun you happen to like as a primary gun. The enemies that are hardest to handle without guns are conveniently not resistant to Elemental damage, and lots of them are especially vulnerable to it. In addition, the monsters that are resistant to Elemental damage are also good at dodging most gun attacks anyway, (except for Chromalisks, but they are pushovers) so going for Normal damage instead wouldn't help since you'd want to use a different weapon anyway.
Alchemers have much faster-travelling projectiles and their specialty is one-hit kills with charged-up contact shots. The Elemental damage Alchemers and Pulsar are all great choices, and any one using guns much should have at least one of those. The Freezing Alchemer is kinda subpar since it can instantly undo its own Freezing effect, but still viable. Pulsar explosions are hard to see through, and pushing monsters around without knowing what you're doing would make for headaches in party play, so lots of people think Pulsar lines are poor choices for party play. IMO though, it is easy to just engage at short range where it does not knock things around or create excessively flashy explosions. You lose some of the bonus damage, but that's nothing compared to what a team mate can do and you're still doing decent damage for a gun anyway. The problem is easy to avoid if you understand it, so don't be discouraged if the Pulsar appeals to you. Having the option to push monsters back sometimes can come in handy, including in party play.
If you intend to use ONLY guns, the Piercing guns are important for dealing with the aforementioned dodgy monsters. If you are comfortable handling Gremlins, Wolvers and Devilites with your Plague Needle, then that should be the only Piercing gun you need. If you have a lot of trouble with those monsters, the Magnus line is your best bet for guns and you should probably try it out after you get your Elemental gun. If you are fine with swords, though, I more highly recommend a Piercing sword- Snarble Barb or Flourish family, they are all awesome.
I have a Toxic Needle and intend to go for an Iceburst Brandish to see if that pair works as well as my Magnus & Nightblade combo, so I guess you might look into Glacius if freezing then smashing sounds fun to you too. If you're buying upgrade slots, though, I recommend a bomb over a sword for freezing since it's much more useful if you can still have at least two other weapons to cover damage types, including at least one gun for reach and one sword for close defense and assault DPS. If you like a Freezing bomb, later on it should be fun to use with a Catalyser...
My answer would be Polaris to both your questions. Polaris is the ele damage as opposed to the Supernova's normal, and since you already have Valiance, there's really no need for another normal damage gun; not to mention, the shock is a nice bonus. Polaris has two things going for it--the knockback and the AOE capabilities. With well-aimed shots, you can hit many mobs at once and keep all of them far away. It's more of a solo gun though, since in party play it both knocks enemies out of reach and blinds your teammates. You can use the unexpended shots, but IMO, the damage is not really worth it when you do that (best party ele gun would probably be alchemer).
If you want a shadow gun instead, you've really got two choices: Umbra Driver and Biohazard. Sentenza is doable as well, of course, but I see you've already got a piercing gun, so the split damage isn't very helpful (people say that the Antigua isn't really good for much outside of FSC too, but I haven't really played with them much). Biohazard feels much like Polaris but without the explosions, and IMO, the charge is kind of dumb to use. Umbra Driver is pretty solid though.
Bottom line, I'd say go for a Polaris first.