I've been to Oahu a few times for work, it's a shithole...West Pacific Island of Commiefornia. Hopefully the other islands aren't as bad, never made it to any of those.
I love Kauai and have another trip planned this year. Kauai is much smaller and less crazy than Ohau. It definitely has much more of a small town vibe and easy to get around (except for traffic, navigation is easy)
I plan on going to Maui and the big island at some point.