Which is the best island group to visit?

Hi,
Travelling to Japan early July, want a weeks R&R on arrival before heading to the northern alps and then the usual culture circuit.
Came across Ogasawara ( bonin) islands as a potential option for chilling, snorkelling and soaking up the sun.
Ferry is 25 hours from Tokyo but can't find a way to book the tickets other than by phoning the ferry company or buying in person from a store in tokyo. Any advice from past travellers?
Second question: is it worth it? Time & cost?
Or should we go to Izu or Okinawa Islands ( or others open to suggestions instead?) Key needs are sun, sand and something to do: snorkelling,walking: not very good at sitting on a beach all day!
also is hokkaido worth a visit? If so where and why.....

How long are you staying in Japan? Ogasawara, I hear, is exquisit, but takes heaps of hours to get there. And you never know if the ferry can be canceled due to bad weather. Worse, if your visit is too short, it might be raining throughout the visit.

On the other hand, Okinawa is famous for having some of the most beautiful, quiet and entertaining beaches in the world, and yet has easy access by direct flights from cities like Tokyo or Osaka.

The best part about Izu is that it's close and accessible by train from Tokyo area, so you can get there with less time and money. But to go to the remote white sand islands of Izu such as Niijima etc., you need to have more time and risk the typhoons. I also hear that it can get overly crowded by young people during summer vacation time.

Hokkaido is a major touristical destination for locals and the climate is pleasant in summer. It depends on what you find is "worth it". It is very unlike the tropical beaches you're talking about.