'Firefly' and 'The Nevers' are his best works worlbuilding-wise

With Firefly and The Nevers i think he really created two worlds that feels 'alive'. They are well described,there are a lot of characters around with their agencies,etc. while Buffy was great with the characters,i always felt like worldbuilding-wise,Buffy (and the spin-off Angel,so the Buffyverse) wasnt really that great. Yes,there are rules,but sometimes the worldbuilding is incoherent and some characters just disappear,like Drusilla for example. Also,some events that happens on Angel,even if big,it seems dont exists in Buffy (like when Jasmine was basically controlling all Los Angeles,or The Beast created a dark sky...was that only for Los Angeles?) so i think altough Buffy is maybe his best works characters-wise,it isnt his best work worldbuilding-wise. About Dollhouse: well that show i think its the most realistic show Joss Whedon ever made,its basically our world,but with a secret agency that creates these 'Dolls',so i guess there wasnt really much you could do with the worldbuilding of that show. But maybe i am wrong.
With Firefly and The Nevers,anyway,i really think he created two great universes,that feels 'alive',so well done.