While I really like 1840 Quentin, and am currently (clears throat in SciFi's general direction) missing him, the prototypical Quentin that we first meet as a ghost is my fave.
First off, he's great as a ghost - really menacing. Then we meet him in 1897, and he's a scalawag, but just jaw-droppingly sexy. Sure, he doesn't get to do much after the return to 1969, but he was great with the Amanda/Olivia storyline and played a good nutcase in the pre-1840 story.
If I'm allowed to separate the different storylines, I'd say 1897 Quentin is my favorite. Again, sexgod, but also he develops quite a bit as a character - making him seem much more three dimensional.
just had to do that - love the skeletons!