WWW or without WWW

My site pr=2 has all pages indexed without the www version .
It is also ranking good for many urls.
Should I redirect naked domain to www one or should i redirect www version to naked one?
Or leave it as it is?
For which one should i build backlinks?

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Tattoo Makeup
Tattoo Make up

i thint that today it doesnt matter www or without www, i see no differences, so it is your decision)
Pedometer for iPhone

There should be permanent redirect between these two sites otherwise the search engine will consider these two as different sites.. better use the www one..

I think www is should applied for your main url for the best link building..