Who should i use

depends on your deck, check out first, on the tier list, and then who gives you more bonus for your whole team.

I would use ssj god because he has the element or color boost

Normally, you should show us your character list if we are to review the characters. However, sp ssj god goku should be stronger than so ssj2 goku yellow as ssj 2 is mainly a support character but he actually supports very few characters. His z-ability only buffs yellow units which are not a strong team as of right now. Although the strike buff he gets when facing Vegeta is a nice niche, most of the broken units in the game are not Vegeta variants and only a few Vegeta characters bear some relevance in the meta. As for ssj god goku, his z-ability may not affect many characters yet but he has great strike damage which can be buffed greater and more easily than ssj 2 goku. Ssj god goku’s main ability also gives an ultimate move which is far more easy to use and master compared to ssj 2 goku’s main ability. Finally, he can gain ki restoration higher than any other character in the game after finishing a combo, allowing you to max your ki much faster than your opponent can often react. Lastly, he gains strike buffs when he is the last man standing, thus transforming from a great support unit to a fast and furious finisher. In summary ssj god goku is better than ssj 2 goku.