It's largely a matter of taste, and no doubt this thread will have a strong pro-Brit bias, but as Indie points out this question is very difficult to answer, especially when trying to make a comparison over the years, unless you have been exposed to TV from both sides of the Atlantic for some time.
From my own experience (having lived in the US for an all-too-short 3 months) I would agree with Indie that the overall quality of American TV is inferior to ours, even taking into account the enormous volume of programmes that are churned out over there year on year. I would suggest, however, that the majority of US programmes that are imported to the UK are of an extremely high quality in terms of their entertainment value, and in many ways could be seen as being 'better' than the domestic products they are scheduled against -whether they are in fact 'better' perhaps being reflected in their popularity with the viewing public?
Whilst I'm sure that some of "their comedy shows, the non rude ones, are terrible", how about Friends, Will and Grace, The Simpsons, Family Guy, Married With Children and Scrubs, to name but a few popular shows that have successfully travelled the Atlantic? Whilst on the subject of popularity we could talk about The West Wing, Ally McBeal, Sex And The City, ER, Dallas (hugely popular in its day) - the list could go on but I'm boring myself now. I'm well aware that one could compile a list of equally popular Brit-produced shows but I'm just illustrating that the US produces a lot of high quality TV, much of it as good or "better" than anything produced over here.
I'm a big fan of home-grown programmes, but I can appreciate that the US is taking an ever-increasing slice of of our viewing pie, and as long as the quality holds up I think that can only be a good thing. Not that I ever get the chance to watch it these days (grumble, grumble...)