Well,
I'm stationed out here on Oahu and the one thing I will say Hawaii is a very different place to live than it is to visit. I love it out here. I'm in a great club and we do something almost every weekend.
If you're in to modding your car there's good news and bad news about Hawaii. Good news there are already two great Mazda clubs out here. Pro 5 which is well established and very tight and M-SPEC which is still forming up but coming together nicely. Bad news is Hawaii's rules regarding what you can and can't do to your cars. Don't get me wrong, we mod, but there is a lot of regs about it. Of course you're coming from Cali so it would probably be a fresh breath of air to come out here.
I can't speak for the other Isalnds, but Oahu is nice. A lot to do and pretty good weather so far. But, I hope you have a job before you move out here. There isn't a lot of jobs available out here and the cost of living is high.
Best of luck on your decision and I hope I have given you a little insight in to life out here.