I like music from all over the world (i mean all!) but in my opinion, the answer is British. You talk about "leaving patriotism at the door" but the simple fact is that the music appeals more to me because I'm coming from the same place as them.
Interestingly there are much more British acts in the top 50 selling artists of America, than vice versa.
I don't really listen to American bands that were popular in the last 20 years, although there is a lot of the classics that I do like.
American music I like:
> Elvis Presley
> Mo-town; like Temptations, Four tops, Jacksons, and some of those others have had great tunes but I wouldnt say I was a fan.
> at a push; Eagles, Skynard and Journey, maybe Beach Boys.
americans have produced some all time classic tunes, but there are very few US artists where I would listen to their albums.
Regarding the "name some british bands and I'll give you their american counterparts" comment someone made, someone asked me that before, I said Queen, they said Journey.
come on!
As for reasons, I blame the weather...many people probably just sit inside and play music or sing because the weather is so shit all the time in England.