It's hard to say, but I am guessing that Ant-Man will outsell Suicide Squad, mainly because the Marvel Cinematic Universe is smoking hot right now. I mean, heck, they took a C-list third-rate team like "Guardians of the Galaxy" and made a runaway hit with it!
(Not just from the hype, either, though that helps -- it was a good film!)
I've been a fan of the Scott Lang Ant-Man every since I first encountered him in Iron Man v.1 #233, back in 1988 -- my very first super-hero comic book! I also really enjoyed Ostrander's Suicide Squad, back in the 1980s. So I shall be seeing both films and hope they are both excellent!