Who is your favourite character?
By a narrow margin, Martin Longbow. He doesn't really have any special "powers" or charisma, and yet he remains as interesting as many of the "larger" characters. He is also the only one aside from Macros, who doesn't count because he's a demi-god, that has a pair and stands up to Tomas/Ashen-Shugar (sorry if that happens in a later book, I've read the entire series 10+ times and they sorta run together).

Did you dislike any of them?
Roland because I so wanted Pug/Carline to work out the first time I read this.

Do you think they're well written?
They are written well enough for this series. I've read several other series with characters that are much more well-rounded, but I've also read series where the characters were far flatter than these.

Does anyone seem particularly believable, or particularly unbelievable?
Particularly believeable or unbelievable? This is high fantasy we're talking about, living, breathing wizards. Of course they are believable!!!