As Ray says, its hard to really get into their Characters cos we only got a limited number of eps, but I always thought that Jayne was, from a female point of view, quite straightforward - a mercenary who liked a good fight and pretty much an old fashioned straightforward male chauvanist pig - altho he was OK with Kaylee being the engineer, but that was prolly only cos he wanted to get into her knickers.
Bull in a china shop approach to pretty much most things
Then we saw a couple of flashes where it seemed he might not be all bad, and maybe even the kind of guy you'd want on your side in a pinch - for the brute force if nothing else
Then came the Ep Ariel and we saw the true colours - a man driven by needs for money and revenge and not a little bit of spite I think. He wanted money, was ****ed off with the Doc and River and saw the ideal opportunity of cover all his wants in the one go. Shame he was so stupid not to think ahead that the feds would just use his info to get the fugitives and then more than likely get rid of him.
So......thats me and me barrow's outside..............