We've got long history at StreamSide, which would take days to reveal, so I'll try my best to provide you with a synopsis.
First, a question, do you really want to be in Vail? Marriott has several mountain resorts, three of which were built by Marriott from the ground up (SummitWatch and Mountainside at Park City, and Timber Lodge in South Lake Tahoe). We love Vail, and we love Park City. For us, Park City is easier to get to, and both Marriott resorts are typical, built by Marriott resorts (in my opinion, a big advantage over StreamSide). Both, Marriott's StreamSide at Vail and Mountain Valley Lodge (Breckenridge) were built by developers other than Marriott, with the exception of the Evergreen Building at StreamSide, which was built by Marriott. So, in my opinion, if you want a mountain experience, you need to pick which mountain resort you want to establish as your Home Resort.
Regarding StreamSide, StreamSide has an eclectic history. The original StreamSide resort was built by a developer other than Marriott, as a purposefully built timeshare resort. The three original buildings were Aspen, Birch and Cedar. If my memory is right, the previous developer started building the Douglas building, than Marriott took the resort over, and I believe completed the Douglas building, and built the Evergreen building, from the ground up.
For quite a long time, Marriott managed the entire StreamSide at Vail resort. In my opinion, there were always factions at StreamSide; there were the original StreamSide timeshare owners, some of whom welcomed Marriott, and some who did not. Then came Marriott, who attracted Marriott buyers, with Marriott expectations, which were not consistent with the expectations of many of the original StreamSide owners. In later years, the Aspen and Cedar buildings ended their management contract with Marriott, are are now managed by another management company, and the Birch, Douglas and Evergreen buildings are managed by Marriott. The Birch building has fixed timeshare weeks, the Douglas building has a mix of floating and fixed weeks, and the Evergreen building has all floating weeks (I've forgotten, there may be some fixed, holiday weeks in Evergreen, I don't remember, but I don't think so). So, in my opinion, in the case of StreamSide, you'd have to pick your medicine or your poison. Personally, I think Vail is a fabulous vacation destination, I am not particularly fond of StreamSide at Vail (for a variety of reasons), with two different management companies, common amenities, and an ambiance that I do not believe is classic Marriott. BUT, if you want to be in Vail, StreamSide may be just what you are looking for.
Of all of Marriott's mountain resorts, SummitWatch in Park City is our favorite. It offers a mix of in-town and mountainside experiences, it is of Marriott quality from head to toe, and the location provides you with direct access to the Park City Mountain Resort, and easy access to Deer Valley and the Canyons.
Mountain Valley Lodge and TimberLodge each have their own attributes, with TimberLodge having been built by Marriott. One of the beauties of owning with Marriott is you have an ability to exchange between resorts, BUT, you should probably try to understand the distinctions between ownership of Marriott's legacy timeshare products, and their newer destination club (points) product.
I've tried to touch on what I believe to be the most relevant points about StreamSide at Vail. I trust that others will add their perspective, and correct and errors or omissions that I may have mistakenly made.