Liz/Will definately, because as space_boy89 said, Liz and Will are both old romantics really. Jack wouldn't be happy with one - he's a-taste-the-whole-fruit- bowl,-not-just-an-apple kinda guy!
Will would make Liz happy coz he's loyal, romatic and strong. Jack's just too wild.
Can't wait for Atonement to come out - Keira looks like she's gonna be great in it!