I think both are rubbish.
ITV show SOME decent shows (Sanctuary, Dollhouse) but let Supernatural go.
BBC have Waterloo Road, and the better news coverage.
I prefer the BBC's sports coverage, as Mitchell said, because of the lack of ad breaks. And they show Rugby League Challenge Cup matches and Superleague highlights. Formula 1 too.
ITV sometimes have boxing and some motorsport, but that's all. Football commentary from both broadcasters is rubbish.
I don't watch any of the soaps.
Against the BBC, I think it is too much geared towards middle/ upper-class office types, kinda like the political system. Except for BBC3, which is just stupid.
I think I watch more on channel 4, than all of the BBC and ITV channels put together.
Then again, Cellcast get 15 and a half hours of viewing everyday!