Hi Cindy. Welcome.
I grew up skiing Colorado, and have spent many a day doing laps on A-lift and Pali. I haven't been to Taos or Sun Valley, but I can tell you about Telluride and Whistler.
Telluride is my favorite town. We have good friends that live there, and so we visit every chance we get. It is amazingly beautiful, old/quaint/historic, typically uncrowded, and super-fun. The skiing ranges from super-steep bumps to easy groomers, with everything in between. I always think of it as one of the more challenging mountains in Colorado. I have never seen it crowded (except for the bluegrass festival in June). The town is great, with wonderful food, great shops, cool bars..etc. I love it. You can't go wrong there (if you go, I would say stay in town as opposed to the Mountain Village).
Whistler is much more of a modern ski village. Since it was all built according to a master plan, it was done well. There are lots of condos, and lots of people, but the mountains are big so it isn't always that crowded. The village is fun, with all the good amenities. Whistler and Blackconb are each bigger than Telluride -- together they are much bigger. Both mountains have incredible terrain - much of it above treeline. I lived in Seattle for three years, so I skied Whistler a bunch. The only problem I have is with the weather. FOG!!! As a Colorado boy, I had never skied in fog. It can be sketchy. On a couple of occassions, the fog was so thick we literally couldn't see my skis. The resort downloaded everyone off the mountain because of it. To facilitate that, the had lifties line the slopes with bells -- as long as you skied down between the ringing bells you reached the lift for the download. Now, I am sure this fog thing isn't that common, but we did encounter it twice out of a dozen or so days over three years (at all times of the year). The other problem was that of all those times, I think there was only enough snow so we could ski to the base two or three times. I loved Whistler, but if you go do some research on the weather.
I am sure someone else can relate different experiences (and tell you about Taos and SV), but if it was up to me I would go to Telluride.
I hope this helps. Have a great trip!