Trip. He was by far the most likeable and the only one who seemed like a balanced, well developed character. How much of that is due to the actor alone, I don't know.
Archer was poorly developed, I feel, in that he was talked about a lot, played up to be someone spectacular, but we never got the SEE any of that, really. He was portrayed as just a normal guy, so the two things didn't really jibe and it became off-putting. I think Scott is a good actor, and I've liked him very much in other things,but I think he's best being the Average Joe, just a decent guy trying to the right thing. But it didn't work with the way Archer was written.
T'Pol did show growth, which I liked, but there were some moments where it felt forced or where playing up her attractiveness bordered on the cheesy. Again, I attribute a lot of that to inconsistent writing.
Just my two cents. Your mileage may vary.