So far I've seen Drake's, Sackboy's, Big Daddy's, Nariko's, Spike's, Sir Dan's, Fat Princess', Ratchet's, Jak and Daxter's, Cole and Evil Cole's and Raiden's. While I don't care for the character, Raiden's color scheme is my favorite. The beige and blue color scheme is very visually appealing.
I'd have to say the least visually appealing character's background would have to be Ratchet's.
Big daddy was the first I saw and probably still my favorite, just nice and simple. The worst is probably the tekken fighter guy's though, the flames look soooo cheesy :/