Aloha,
I have been living on Oahu for almost two years now. There has only been one time I remember the vog being really bad - to the point where my throat felt funny after being out walking. The other poster is right that if we have vog it is usually only for a day or two before the winds blow it away. It has not been an issue for me or my family.
I love Kauai and it is very beautiful and lush. We visit there regularly and I would consider retiring there. If I were young and single it would not be my first choice, but I think it depends on what you are looking for. If you want a small community feel it could be right for you.
Oahu has some beautiful, lush areas too - think North Shore since commute is not a factor - and also has access to downtown Honolulu with lots of restaurants, nightlife, shopping, etc. We also have the Honolulu Symphony and Opera and many plays if you are into that.
I really like Oahu - I think it is under-rated in a way. People think Oahu is only Waikiki - but it has so much more to offer.
I also agree with the other poster to rent for six months and see what you think before committing to a longer term rental or buying something.
Best of luck to you!
