Typical scenario, eff stacks 100bb.

Hero opens 3.5bb with ~JJ/QQ/AK, Fish IP 3bets to ~12bb, Hero?

I typically 4bet 2.5x to let them shove worse and to maybe get called lightly where as betting bigger may scare them off. A common issue I'm facing is having to play OOP in big pots and c/f when overcards come or give up when I whiff AK. I feel really dumb when they call, flop comes Axx, they bet 1/2 pot, and I'm like lolcheckfoldaments.

Arguments for sizing smaller: induce much lighter calls, induce more bluffs/reshoves, pot is more manageable on the flop.

Arguments for sizing bigger: more immediate value, hand plays itself on the flop for the most part (tho we still need to play some guessing games, but hopefully less than normal).

Sizing bigger seems better to me since they're fish and will stack off light, but what is your standard? 2.5x might be totally fine and I'm just frustrated from recent sessions but this is a spot where I feel really uncomfortable on a daily basis so I figure I might be doing something wrong.

This is definitely a spot that I have some difficulty dealing with, and I'm surprised it hasn't got more/ any attention yet.
Firstly, some info on how each fish deals with 4bets (either notes or fold to 4b stat) is extremely helpful as this will vary a lot. If they are not folding at all then you should just be 4betting the maximum you think they will call. In some cases, (this applies mainly to AK) I will make a big 4b to around 30-40bb, leaving them with a pot size bet behind and just shove any flop. QQ I feel plays well enough post flop to take the standard 2.5x line against the majority of fish. With hands like JJ/TT/99 oop, if villain has fairly loose 3b stats then just shoving is also fine. You'll fold out a lot of hands that have equity against you like KQ, KJs etc, you're not doing badly against their calling range, and not losing too much value as most people don't 3bet their 22-88 IP very much.

depends on what you have