January - Okinawa/Ishigaki vs Sapporo

We have 6 nights of our Japan holiday in January to do either of these, or both! Initially we were thinking 4 nights in Okinawa and then fly to Sapporo for 2 nights, but would really like to know people's opinions.

We kinda like the idea of Ishigaki or Miyakojima rather than Okinawa itself but worried we will get a little bored. Its not like you can sunbathe on a beach in January!

Swimming with turtles would be pretty great!

Advice please on flying to Ishigaki or stay in Okinawa?

Not sure what is in Sapporo or if it would even be worth it for 2 days?

Please help us decide.

Thank you :)