One of my biggest long-shots is Will or Georgia in the end. They're one of three couples who have been (and, presumably, always will be) in a stable, loving relationship since their introduction to the series. It's them, Michael + Charity, and, to a lesser degree, Thomas + Justine. I say Thomas and Justine are loving, but not exactly stable, and their relationship seems to have been started mostly due to codependence, especially on Justine's part.
My other long-shot is Amanda Carpenter. My reasoning is that A) it would be nice to see a Carpenter Knight once again, B) we haven't had a permanent female Knight yet, and I think the last one will be female, C) Daniel is kinda too obvious, though he's also pretty clearly not fit to be a Knight without some serious character development, and D) it would subvert expectations for the Last Knight to be a character who'd received so little attention early on. I do think Amanda will need some more attention, and if she starts getting some, it'll feed my WAG even more.
Obviously, Daniel could be currently undergoing tons of personal development (I think he joined the military, so he'd presumably pick up some discipline if not necessarily a cooler temperament) off-page that we simply haven't seen yet. It's entirely possible that the next time he shows up he'll have chilled out a great deal, and would make a good Knight.
Anywho, those are my picks within the current State of the Series. I'd like it to be Will. Or hell, Georgia. Her current status in the series is basically Professional Kidnappee, so it'd be nice for her to stand on her own two feet.