I decided this based on sheer math. Water Rifle --> Ice Hammer Special = 110, Water Pistols --> Ice Rifle Special = 120.
This is probably bad-ish math because Water Rifle 30 + 110 = 140, Water Pistols 20 + 120 = 140, and the latter is less reliable because the pistols miss more, but it looks cooler. For double specials: Water Rifle 40/10 splash + 110 = 150, Water Pistol Special 40 + 120/10 splash = 160. So the latter combo does give you a slight edge.
Unfortunately Water Rifle + Ice Hammer hit = 70, and Water Pistols + Ice Rifle hit = 60. So if you're bad at spinners, the rifle + hammer combo is probably more effective, but you sacrifice max numbers for reliability.
Rocket Hammer special is 65 to Ice Hammer's 55, so it's more effective. The Ice Gauntlet trumps the Vambrace because it doubles under water use, and it it is devastating against Cogra W37s. Fire Cane is essential for fighting Bigfoot, the Grease Pits, and other ice enemies.
I'm pretty sure this is the most powerful loadout in the game to date. It doesn't help me though - I still am terrible at battling, so...time to get out the dynamite. Again.