Well in general, you can seperate Thor's teammates into like three categories:
1) Teammates that help Thor approach
2) Teammates that help Thor do combo damage
3) Teammates that Thor helps
Category 1 would be characters with moves that can get the opponent in continuous blockstun like Dr. Doom's missiles, Ironman's beam assist or Akuma's tatsumaki assist. There are many more options but these are just examples.
Category 2 would include assists that can help Thor continue combos for more damage like X23's ankle slice or Wesker's samurai edge assist since these assists pick the opponents up off the ground for Thor to continue piling on the damage.
Finally, Category 3 would include characters that Thor's assists help. A strong point character like Zero or Magneto with no ability to ground bounce a character for longer combos would gladly welcome Thor into the mix.
Of course there's an option we haven't discussed. The last option is putting Thor with a gimmick team. In the end, the game is about fun. So some people will want to run teams like Gimpyfish does.
So who would you like to team Thor with? Or do you think Thor does better being thrown on other teams rather than having teams based around him?