Weasel looks terrible, so from that standpoint I hope he's one of the first into the grinder.
And while I'd love to have blood sport around for most of the movie, because I like Elba, I can appreciate the idea of feeding one of your biggest headliners into a wood chipper in the first scene, because "**** you this is suicide squad".
I expect Fillion to die quick, as he's not a long action movie kind of guy, and his character seems made up for this film specifically. (I envision a phone call along the lines of, "Hey Nathan, want to come in for 3 days of shooting, be a dorky supervillain, make a couple grand, and film a comically gruesome death scene?")
Thinker seems custom made to be first or second to take a dirt nap; he'll believe he's figured out a way to escape the team, and he'll end up as a gore soaked scorch mark.
Peacemaker looks goofy enough, and his schtick doesn't fit the theme, so I assume he's not long for the world either.