Sun Island or Zhaolin Park

I am planning to visit Harbin the first week of February 2018 and to go to the ice festival. But I see there are two venues, one at Sun Island and the other at Zhaolin Park.

- What is the difference between the two and which one would you recommend to visit (if you have to choose one)
- For how long is a ticket valid?
- May I exit and re-enter with the same ticket on the purchase date?

Thank you once again