I chose McKenas Cole and here's my reasoning...
#1 Quetin Tarantino is a great Hollywood director/not so great movie star. He can't be on the show forever. Though I'm sure he wouldn't mind the guest star spot every other year.
#2 I'm not a fan of Lauren. But you're not supposed to be. I love the character though. Relationships on TV shows die out if there isn't some barrier put between them every once in a while. It's the anticipation of a reunion that keeps the audience going. Plus, the show was definitely losing its "bad guys" left and right. Irina seems to be good in her own way. Anna Espinosa is MIA since Season 1. Evil Francie has died for... what... the third time (Bet you she comes back!). The Alliance and Sd-6 are gone. Jack killed Simon Walker. For the love of god, why do the bad guys keep getting killed and we haven't had any good guy casualties (except for Bradley Cooper leaving the show. But we have the hope of guest spots still with that).
#3 Sloane can't die. He's the granddaddy of Alias bad guys. Without Sloane, the show would suffere. He doesn't have to be in an episode a lot. You just have to remember he's out there with some plan that you have no idea about.
#4 Sark... ahhh... he should never die. Brings a much needed funny cuteness to an episode. His character still hasn't been fleshed out completely. I want to see that... (BTW- Glad to see he has no votes. You might dislike him or dislike the idea of him being with Sydney, but you have to admit, he brings a little somethin' somethin' to the show).