There was a period about 7 years ago where they were fantastic, their 3G/4G network wasn't too bad unless you were out in the sticks, and they were CHEAP, about 13£ for 200 mins/200 texts _unlimited_ data. And the kicker was pretty much unrestricted high speed roaming.

Have since moved over to EE which is better performing and better coverage but much pricier. 3 sadly will fall over in the next couple years I would bet.