The Suicide Squad are made up of a group of villains. A hardcore group of villains. So when I read that Movie Pilot wanted writers to make their team own team, I decided I needed a team that could fit in and be effective in every situation and be as ruthless as needed.
Every team needs a good goon. The Fantastic Four have the Thing. The X-Men have Colossus and this team has the perfect goon; Jason Voorhees. A near unstoppable killing machine is the perfect guy to send into either be a distraction or keep a guy busy while the other team members come up with a plan or escape to fight another day. And if he dies, don't worry, he will probably be back in a day or so. He's probably the best teammate because he wont give you any back talk. He will just kill stuff and keep killing stuff. Jason was the second person I thought of when I saw this contest. His only downfall is that he doesn't really seem like the type to take orders. Good thing the next person on my list can make something to control him.
You also need a genius and there aren't many that come smarter than Victor von Doom. Actually, the only person who might be smarter than Doom is Reed Richards. The biggest bonus is Dr. Doom is he is well versed in the mystic arts on top of his superior intellect. So even if his weapons fail because the team is fighting some demon or some other supernatural being, Doom will have something to counter that. Doom's flaw is that he doesn't always play well with others. So with a team Doom is on, he has to be leader and everyone else on this team must follow his lead unconditionally.
Also needed is a skilled killer and fighter. It's all good to have Jason as an unstoppable killing machine, but you also need be stealthy at times and also someone who has actual fighting skill. You would assume a guy that big couldn't be as stealthy as he is, but if you've seen the movies then you know what he does. If you haven't, he is not only surprisingly light on his feet and has tech that makes him nearly invisible. Predator is all about the hunt so I don't really see him sitting through many mission briefings. Doom will almost definitely have to control him too.
Lastly, it's always good to have a guy on your team that can kill a god and the Sentry has killed two (Loki and Ares). Sentry is easily manipulated and sometimes seems to have no idea what's right and what is wrong. So getting him to join a team won't take much. Downfall? He is bat poop crazy. But as long as you don't touch his wife and make sure you keep his dark side happy, he will pretty much do whatever you want.