Peyton.. well i really didn´t pay much attention to her..
Lucas grew a lot.. he finally made up him ming and finally decided what he wanted.
Brooke got over her insecurities...
Haley.. well haley was always the mature responsible one IMO
But nathan.. went from badboy jock to an amazing father and husband

To me, it was a tie between Brooke and Nathan but I ultimately picked Brooke. Nathan has done a lot of growing himself.

Brooke.....Nathan......Haley

Nathan hands down not that the rest didn't he just went from bad boy to father and it was awesome.

definitely

brooke grew then took two steps back imo

brooke grew then took two steps back imo
Exactly my thoughts. Brooke grew up a lot in seasons 5&6, which is why I started to enjoy her character a lot but in season 7 she went back to being her insecure and childish self:/
Peyton&Lucas did a lot of evolving by the time season 6 came around as well. Peyton started to trust and let people in and Lucas stopped hiding his heart. To people this may not seem like a big deal, but that was the main issue the two characters had.
Haley evolved a little, but not all that much. But as mentioned above Haley's always been the mature one.
So by far Nathan. He went from being an ass who didn't give a shit about anyone, to being a loving and caring husband.

haley didn't do much as evolve as gained confidence and simply matured naturally with age.
lucas i think was better off at the beginning of the series than how his character ended.
imo peyton didn't evolve at all, her main issues were never dealt with.
i would have voted brooke by far if it wasn't for s7-9.
all up it would have to be nathan, though his initial evolvement was quick there was def more growing up and such as he got older and you could see the way he'd changed with how he dealt with things at the end of the series compared to the beginning.