I've been to the 3 Valleys several times and there's nowhere else to match it (not even the EK where I'm off this year again).
I'd take on baord the point about it being less than prettty - but it's a lot better than people give it credit for with a real effort to makwe it more "sympa" and it's never been as bad as
Les Menuires or Stalag Luft
Tignes.
For pure skiing then it's unbeatable - lack of trees can make it cold but then winters have become so unpredictable that that could be said of anywhere.
My only caution would be to echo the point that someone made about some of the intersections being very busy - my wife got seriously hurt at the bottom of the resort and the run down to Town from the Club Med area is carnage at 4pm
I can't comment on
Morzine as I've never been but have heard many good things (though some of the interconnectuion is meant to be less slick than 3V etc)