Mobile Phones - o2 or Vodafone

I was planning on getting a new phone for christmas but there is a few which i was looking at and was wondering which one is the best value and which ones people have had problems with, the phones i was looking at are: Nokia 6600 Slide Nokia N96 Nokia N95 Nokia 7610 Supernova Samsung F400 LG ViewtyMobile Phones - o2 or Vodafone
i'd go for the nokia n96 simply because it's the updated version of the phone i already have. o2 and vodafone are pretty similar in terms of service, cost and reception but o2 also does some great deals on iphones if those are your thing