4 days on tongatapu

Hi my wife and I and our 9 year old son are going to Nuku'alofa for four days for a budget holiday. what are the good places to stay? We just want to swim and relax, maybe fish, whale watch go in a glass bottom boat. We've been to Samoa (5 yea4s ago) and wonder how it compares?

Head straight to 'Eua-4 days in Nuku'alofa is 3.5 days too many.

Somehow I don't think Nukualofa is going to match up to expectations. Most people seem to be dissapointed in it. Other parts of Tongatapu can be nice (depending on what you are seeking), but the vast majority of people use it as a stepping stone to Vavau or Haapai (for a reason).
Whale watching, snorkelling etc are typically done on these other islands groups.

With only four days it will be pretty tight going to Haapai or Vavau, as the flights can be unreliable, and there are none on Sunday. Eua is not far, maybe better to check that out. Also, as you are on a "budget" holiday, the airfares to Haapai and Vavau might be higher than you really want to spend for just maybe two days.