Months to come here, less rain, less heat? Those are mutually exclusive. Winter is slightly cooler, but more rainy... roughly Nov - March. The windward sides (genarally eastern) of all the islands are rainier/cooler than the leeward sides (generally western).

Which island is the best? Hard to say. My preference is the Big Island... Here's some general vibes.

Oahu: urban, busy, commercial, lots of "tourist attractions". Lots of gorgeous white sandy beaches. The beach babes spend a lot of time on the tread mill. Good for cultural exploration, museums, and a variety of cuisines.

The Big: Big, down to earth, slow pace, lava. Don't expect the locals to do anything real quick like. It's the least densely populated island. Not so many tourist attractions outside of natural type things. Kona sucks, but there's some "good" luau's on that side. Beaches are more rugged (they're younger), not so many white sandy ones. The beach babes wear their Kalua Pork with pride.

Maui: Small, spendy, exclusive, stunning natural beauty, suburban. Great for surfing. The road to Hana is trecherous. Fill the tank before you go!

Kauai: Very small, pretty down to earth, small town feel. Great hikes, kayaking. Good traditional beaches.

Lanai, molokai: Very small, exclusive.

Ni'ihau: Forbidden. Go above the high tide line and... pau.

I hope that helps you get some idea for where you would like to go.

Enjoy, aloha,
mikeT