Personally I rate Buffy as the best of all Joss' series and it's success in terms of popularity and longevity testify to that. I'd say;
in terms of preference.
I agree with Buffy on the top of the list. I'm a big Joss fan too, and it is the most impactful and long-lived, pop culture wise, of his shows. It has contributed some of the best episodes of TV history, in my opinion. 'Restless', 'Hush', The Gift', 'The Body', these are truly superb hours of TV by any standard.
Angel is a close second. I just love the Buffyverse, full stop. Angel is a darker series, and twists the Buffyverse mythos on its head. In some ways, its like the DS9 to Buffy's TOS (I see more in common between Buffy and TOS than Buffy and TNG. Buffy is about a mix between strong characters, action adventure, drama, and the occassional deep, thought provoking ep, just like TOS). Angel is also a great series, but in a different way to BTVS. It perhaps doesn't have as many 'stunning' episodes, but its still awesome.
I think you're maybe a little uncharitable towards Firefly, Saturn. It was also a very well-made series (what little we saw of it), and had the potential to become another Joss classic. I don't think its fair to compare it to AtS or BtvS, because it simply didn't have enough time to grow. If Season one of Buffy was all we got, it would have ranked very differently in my list.
I haven't seen the webseries Dr Horrible yet, and I haven't seen enough of Dollhouse to properly judge it.