I think either Maw or Corvus takes the top spot on this list. Maw gains mind control on his third skill which makes most pve content super easy mode and Corvus gains tons of buffs like his 5th skill buff, his 25% all attack from his uniform and additional 15% physical attack from his uniform passive which helps both him and his clones. I would say choose Maw for PVE and Corvus for PVP.
For the third place, I would rank Proxima. It adds i-frame to all of her skill which covers her survivability problem she use to have. Black Widow, Hulkbuster, Starlord, Rocket comes after that. There’s no particular order here since I think they are all in the same power level. Pick who you like the most but personally, I would stay away from Black Widow, Rocket and maybe Hulkbuster because they will likely get a new uniform for Avengers4 next year.
I’ve executed Groot. It is definitely the worst uniform among the infinity war uniforms and just not worth the 1050 crystal cost. His Baby Groot uniform is arguably better which is saying a lot. Stay away from this one.