It seems to me you now have loads of info about 4 different areas. Up front I'll have to admit I've never been to Chamonix, but the friends I ski with have. I have skied all of the others & worked in one.
The biggest thing that you'll notice about the French resorts is their size. While in the US you generally measure resorts by acreage, in Europe we measure trail length. In all but Chamonix the lifts are linked and the areas are truly huge, even in comparison to Vail.
Many european ski resorts grew up around mountain villages in valleys but in the 50s & 60s, purpose built resorts started to be built up above the tree-line, where the snow was more guaranteed. The down side to this is that the purpose built villages are often made up of high rise apartment blocks, quite soul-less & when compared to the original villages lower down. You generally have a choice: lower price, self-catering, ski in/out, purpose built "boxes", often only bookable by the week, or more picturesque resort, hotels, restaurants, a bit of a walk to the lifts & flexibility in trip duration.
Portes du Soleil (Gates of the Sun) is the lowest of the three & spreads over 12 villages across the French/Swiss border. The southern edge (Morzine/Les Gets) doesn't link directly by lift, but a short walk across Morzine town centre to the superMorzine bubble, or a three minute bus ride to the les Prodains Cablecar takes you directly into the rest of the area. I've skied Les Gets/Morizine the last two years & there's been plenty to keep us occupied, but Avoriaz (the imposing purpose built bit) and beyond is a great area that includes the world famous Swiss Wall - once rated as one of the ten toughest runs in the world along with the likes of Corbet's Couloir at Jackson. This area is only an hour or so from Geneva and boasts over 600 kilometers of trails.
Espace Killy (Val d'Isere.& Tignes) is another huge area. Tignes accomodation will be more affordable than Val, with the same ski area that includes a smattering of Olympic ski venues, but as it's the purpose built bit, it's not as pretty. Tignes is made up of three "villages" Lavachet, Tignes le lac & Val Claret. Val Claret is the most village-like and is also the highest so most snow-sure.
The 3 Vallees is the highest skiing in Europe with Val Thorens as the highest accomodation. Both it and Les Menuires are high up & purpose built on the right of the area as you look at the map. Meribel, in the middle, is more traditional and has a lot of smaller chalets while Courchevel (split over 4 levels) covers the left of the map. Courchevel 1650 would be my personal favourite - close enough to the glitzy 1850 for you to mix with the "beautiful people" & the jet set, not too purpose-built and fairly accessible to the skiing. More reasonable accomodation can be had further down the valley in the historic spa town of Brides-les-Bains, with 2 VERY long gondola lifts straight up to Courchevel.
Bottom line, as you've already said, you won't be disappointed with any of them, as long as you do a little homework. With the size of the ski areas, and if you're on a typical American couple of day trip rather than a typical European one, you may not even cover the whole area in your vacation. You might consider a day in Morzine/Les Gets then a day in Avoriaz, or a day in Courchevel and a day in Meribel/Val Thorens. If that was you thing, the n Cham would be equally as good as you could ski a day in each distinct area and you wouldn't waste time moving from area to area.
I also post on a European forum that's similar to this one - www.snowheads.co.uk
It's definately worth a look.
Hope the snow gods are kind & don't forget your shades & sunscreen.