Personally, I like Braum more. As a supp it's important to set up plays and I feel like Braum's ult does that better. A blitz grab just gets a pick, but if your team has no other engage, they can just walk back to tower and wait for the player to respawn. Also, blitz is a snowball champion. If you win lane, blitz it amazing. If you lose lane and your team is losing, often times grabbing someone and pulling them in is a death sentence as the rest of the enemy team goes in. It depends on how far behind you are though. But I also know what you mean, a good blitz pull could potentially win the game if all goes well. I'd say look at the team comp. One thing nice about blitz is he can go AP or tanky, Braum can only go tanky really...