Best Islands to travel?

Hya there
I am now in NZ, considering a trip to the Islands around April or July (before or after Oz).
If I have to choose about 2-4 destinations, what would be your best recommendation, from Tonga, Samoa, Vanuatu, Fiji, Cooks and the list goes... Important parameters are dive sites, expenses, flight connections between islands and stuff for young travellers... (girls, beers, backpackers, y'know)
And do you think the prices will go much higher around July or is it still the same as in April-May?
Thx
Shamir

I think the further you are from PNG, the poorer the diving gets - so of the countries on your list, Vanuatu has the best diving.

Costwise Fiji, Samoa and Tonga are the cheapest ones, Vanuatu probably the priciest.

For the girls/beers scene for young travellers, it's probably Fiji - the others much quieter.

Fiji is well connected by cheapish flights to Vanuatu, Tonga and Samoa and easily combined with any of those.
It still has a link with the Cooks too, but that may not last beyond April or so - anyone knows the latrest on that?

Fiji--Cooks--Fiji is still once a week, no plans for that to change as far as I know.