It really depends where you are. 3 claim the strongest network and they recently upgraded the network locally but I saw no difference, but from being a customer for 7 yrs and hating their appalling India based customer service, I left last month and am now with Voda whos 3g is more stable and faster in my locality.

Not saying it is where you are but I did try Voda on a sim month by month deal to check it out alongside 3. Its far better.

In my experience their customer service is a mile better than talking to 3 that are based on the other side of the world and read from a script and can barely comprehend what you are saying!

Although I do know someone who had a fraud on their voda contract and has had a nightmare trying to sort it out.