My ultimate badass suicide squad would mostly consist of characters based on their abilities. I will base them on possibile scenarios. Also on who'd work well together and who's just badass on their own.
ANTMAN (SCOTT LANG)
I know he's considered more of a hero but he did start out as a criminal. Naturally I chose him instead of his predecessor Hank Pym because he's not a total douche. Plus Scott strikes me as a team player willing to work with whoever. His shrinking abilities can come in handy if a mission required stealth or if the team ever got captured he'd be able to escape. Plus he's trust worthy enough to not have to worry too much about him betraying the team. His criminal past will come in handy if the mission had anything to-do with a heist. Over all he's a great team mate for the squad.
Ofcourse you would need rocket his skill set is excellent for all sorts of missions. He's a weapons expert creating all sorts of weapons and explosives. He's a genius when it comes to planning coming up with all sorts of crazy plans under extreme pressure. He's escaped tons of prisons incase the mission is almost compromised we know they'll be able to escape and get back to it. Technological master he'll be able to hack into almost anything. He's not much of a team player but under the right lead...
Red Hood (Jason Todd)
Now the leader must be trustworthy and Jason is not the most trustworthy guy ever but he gets the Job done. His skills include hand to hand combatant (trained by the Dark Knight himself) and acrobat. He has a small amount of detective skills which could come in handy. His weapons of choice are two pistols and a knife. He also wears a bullet proof vest just thought it was worth mentioning. I chose him to be the leader because he has lead his own gangs. Knowing that gangs can be tough to handle he must have he leadership chops.
You can't have a suicide squad team without Harley Quinn! She plays the wild card she's so unpredictable not even Joker can guess what she'll do next. She carries along with her a large hammer to smash her enemies. Her past as a psychologist could come in handy for when a mission involves Arkham Asylum.
So there you have it my Suicide Squad they would make the ultimate team. Any task they've got it!