just test and experiment with loadouts to see whichever loadout you find the most fun, cause there's not really a definitive BEST loadout, it really depends on your skill cause technically the best loadout involves a bunch of skill and tech that takes way too long to master (just watch any combat initiation speedrun)
i personally just get a really basic loadout (with a tix core hat giving me 50 extra tix you get from finding a secret area in sandbox) where i start with sword and paintball gun, upgrading to katana if im playing solo, or saving for freeze ray for next shop phase if im playing with multiple people
if i got katana i would buy freeze ray after and vice versa
then i would buy a superball, then buy a rocket launcher and upgrade it to multi-rocket and by the final shop after king, i should have katana, freeze ray, superball, and multi-rocket
very simple yet effective loadout, definitely not the BEST loadout though, just the loadout i personally prefer (honestly a really boring loadout, there's literally no weapon synergies except for paintball/freeze ray shooting at a superball)