I would personally steer clear of 3. I've just ended an 18 month contract - and it couldnt have ended soon enough for me. Sure you get your free minutes, but they are for use in the UK only, and so are the free texts. My bills shot up with 3 to over £150 per month!
Now I'm back with O2, and I should never have left! I pay £40 per month and for that I get a gorgeous phone, free calls on Saturdays, Sundays and Mondays, then 750 free minutes to use for the rest of the days in the month. Plus 1000 free texts. The good thing about the texts is that unlike any other network in the UK, when you're abroad and you text home it takes 4 of your free messages rather than costing you more!