Quick Survey on Tank Supports in 2v2

Let's get straight to the point. You are in a custom 2v2 Howling Abyss Tournament, and you are paired up with a person you don't know against 2 people you don't know (Duh!) Your teammate says that they only know how to play Braum, Blitzcrank, Thresh and Tahm Kench. (So basically they are support mains) You are going to be the carry and you will choose what champion your teammate will pick. Who do you tell them to pick and why? Would be extremely helpful to leave reasoning for your picks in the comment sections below since I am planning on buying one of the 3 champions, and I AM going into a 2v2 tournament quite soon.

Edit: The tournament is Blind Pick, just in case you were wondering. Telling them to play their best champion is also not an option.