Gladly this game rewards skill much more than gear. Perhaps there will come a time when different equipment sets are necessary, but right now just complement your fighting style, try not to have negative resistance against fire or shock, and master your style of fighting.

The supernova, but get a polaris dirt if you don't have one.

itd be good to just test the cheap 2 star versions of the guns in this case

pulsar - explosion - knockback in all possible directions
magma driver - elemental+fire - can light oilers
valiance - normal+knockback - i dont see any issue or disadvantage with valiance

Polaris is best, especially in FSC. If you don't want that the knockback from the Valiance is excellent.

Which gun is best depends on what you're doing with it.

One nice thing about the alchemer gun lines (which includes magma driver) is that you can spam them on anything without messing up teammates, because there is no knockback. It's very, very annoying to try to melee a mob that someone else is spamming a gun with a knockback on, constantly knocking it out of your way, or knocking it into you so that you get hit even when you properly dodged it.

Valiance has a slight knockback, even though the lower star guns in its line do not.

Polaris, on the other hand, has a larger knockback, along with a huge, flashy explosion when it hits. Both of these can be major problems. The knockback is a problem for the same reasons I described above.

The flashy explosion is often a bigger problem, as it makes the mobs effectively invisible for a brief period of time. You know how a lot of mobs give you some sort of warning that they're going to attack? A polaris explosion covers up that warning, so that the mobs effectively don't warn you when they're going to attack. Thus, your teammates have the choice of either going suicidal in trying to attack it anyway, or getting out of the way and letting you solo it. If that's the only mob available to attack, then that means letting you solo, period. If you spread your fire among several mobs, then you get to solo all of them, or maybe die if you're not good enough to solo all of them at once.

Even if a gun looks like it does good damage per second for you, if it means that teammates who would otherwise have done more damage have to lay off and leave you to fight it alone, then on net, you're getting negative damage per second. That's not good.

Now, polaris isn't horrible like that against all mobs. Against some mobs, every single hit interrupts the mob. This is most notably the case against turrets. Turrets are also impossible to knock back. Thus, polaris works great against turrets.

If you're careful about it, it can be a nice gun. But if you spam it on everything while you're in a group, then you're doing more harm than good, and really deserve to be kicked from the group for being an idiot.

With any of the alchemer guns, you can spam them on nearly everything and its fine. You don't want to light oilers on fire with a magma driver, freeze ice cubes with a hail driver that someone else has melted, or shock quicksilvers with a storm driver. And you don't want to pull mobs that were minding their own business. But other than that, you can spam it on mobs that someone else is meleeing, and it doesn't cause any problems.

If you are not a dump spam shooter with the Polaris, it's the best weapon, for solo or teamplay. if you really learn to use it, like when it explodes or such things, you can push the mos where YOU want, and not "in all directions"...

I loled at the sentence that a Valiance deals more damage than the Polaris. No way, mine does 250 damage at deep 28 ... well got 2 tinkers, normally it's 190, but the Valiance still just reach 100. Also the Polaris deals 4x 30 Shock damage wich are additional 120 and don't forget the shock goes on unaffected near mobs too and will stop their attacks, especially ghost kitties will cancel while charge.

Polaris >>>>>>>>>>>> Valiance, in every situation expect against Wolver or Gremlins. Making a Supernova cause of this is a waste of the superior shock and bonus damage against many mobs.

A somewhat random but still heartfelt request: PLEASE do not whip out an alchemer without warning in an explosive-block-heavy area when in a party. As a swordsman, I like to use explosive blocks for extra damage against enemies, which means I am frequently in the middle of a bunch of blocks. I can keep my distance from any gunners' lines of fire, but alchemer ricochet shots are another matter entirely. Somebody I randomed with decided to switch from a polaris to a magma driver while I was deep in one of those rooms, which resulted in a highly unpleasant experience.

I'd say storm too, as I have one myself and it's my favourite weapon. I've never used a magma driver but I'm a fan of the fire status too, and as both guns have one enemy you really don't want to use it with (quicksilvers or oilers) I expect they're practically as good as each other. Storm just about edges it for me, but both are good choices.