it's very interesting to read all those opinions. i never really thought about this...
but now i think it's john... if you can rate it like that. to me he always seemed like the most "extreme" character. fallen from one opinion into the other, very quick without being interested in what he said 2 months before. the very optimistic man, the drug addict, the love-and-peace-hippie and the angry rebel.... whatever, there were a lot of pretty extreme sides in him at the same time... always i think. not able to find a middle where he feels comfortable in for a longer time. so i don't think he changed too much, that was part of his personality i guess... always was.
george is different for me... he changed a lot too... but he seems more like a guy who found his direction. and stuck with it the rest of his life.... like he just searched for this change, found it and was happy with it. end of the story if you want to put it really simple. but in the end i think it's also something that has always been in him and he just found it... so you can call it change, sure... but i don't really think of it this way.
paul progressed in his life too of course, as has ringo (i guess) but for someone like me standing outside it doesn't seem as extreme as the other two.
it's way too early and i shouldn't spend my time thinking about this, i should get ready for work...