Fiji/Samoa/cook islands at the end of a RWT?

I'm looking at going to either Fiji, Samoa or Cook Islands at the end of a round the world trip but I don't know where to choose; they all look great!

I'm planning on being there about June/July 2013, and becuase Ill have been doing some real exploring/volunteering round south east asia/australisa im looking for somewhere to relax (a proper holiday before i go home) but maybe to meet other travellers as I'll be on my own and to do a bit of exploring if the mood takes me. just wondered if anyone could help me on the following

1-weather - which island is the best? I'd really like to guarantee some warm weather so i can swim in the sea and I've read it can vary from 18 degrees to 26 degrees in June/July? Has anyone had any first hand experience?
2- costs - which island is the cheapest for back packers? I hear varied reviews!
3- which is more geared to back packers? I guess I'm looking for somewhere fairly unspoilt but not a ghost town!
4- all the islands look stunning but is there one which stands out and has the most interesting scenery/geography?

Thanks for your help in advance! Really struggling with where to pick!

Malo WednesdayFlowers

I live in Samoa, but know Fiji well and know about Cook Islands from locals I have spoken to.
In a nutshell, Samoa is best for cultural experiences; Fiji is best to enjoy the resorts on the outer islands and the Cooks are a lot smaller with less opportunities, more of a happy holiday.

If you want to volunteer in Samoa, there are two opportunities that we do for short-term voluntourism in Samoa (WWOOFing and SWAPing) www.wwoofsamoa.com and www.swapsamoa.com. Opportunities for Village Stays (www.samoavillagestays.com) will open up when/if you get here.

The cheapest accommodation in Samoa is at Camp Samoa (www.campsamoa.com) which is $30.00WST per night food and accommodation with rebates available for volunteer work completed. It's rural and really budget but a real Samoan lifestyle experience. Outdoor living on the plantation at it's best!

Fiji is the cheapest and the most geared to backpackers by a very long shot.
It also has far more islands (hundreds!), and far more diverse ones, than either Samoa or the Cooks.
It also has good weather in that period.

A pretty obvious choice to me.

I'd agree with Lazlo on Fiji...

In order to be a good backpacker destination you have to have a combination of cheap access (like the international hub that Fiji is) and be attractive enough to have people want to spend time there.

Once you have that, you'll have enough traffic to have the economy of scale that makes sense for niche businesses, like hostels, etc, to flourish.

The combination of easy access to Nadi, fairly cheap transportation to the Yasawas and some high-quality backpacker places there, make it a great bang for the buck.