To be honest, my answer to this changes pretty regularly. When I first watched them, it was BTVS hands down, but as an adult I think I appreciate Ats' grittier tone far more than I used to.
These days, it just tends to depend which show I'm watching most... and at the moment, I'm watching more Angel.
But they're interchangeably first and second place in my favourite TV shows.
See.. the humor is exactly why I dislike Buffy. I do not mind the comedy episodes, per se, just the general comedy tone I did not like. The dry wit as in the first two seasons of Angel (and less as Joss took over) was more to my taste. Brief rant... Cabin in the Woods would have been much better had it not the 'Joss' humor with it. Thats what devalues Buffy in my opinion.
Angel is not for everybody especially for those who want the lines between good and evil to be clear and to not mix with eachother. Angel is just a more mature show.I'm pretty jealous of all the people that really love Angel. I just can't seem to get into it at all, though I've never really been too much of a fan of Angel the character, personally. I'm not sure why.
BtVS wins for me!