First of all, I highly recommend FTI for the best 737 type training at the lowest price, so I think you are making the right choice there (no I do not work for FTI!). I am sure other places do a fantastic job, but for the money, you can't beat FTI.
Anyhow, I went to the DEN location, and it was a very good experience. The sims are UAL sims, in their training facility. You get "gentleman's hours" since no one besides FTI uses the -200 sim. The instructors are all UAL pilots/instructors, and very good dudes. Their offices have a cardboard mockup you can use at any time. The offices/classroom are not fancy, but utilitarian and get the job done. They will prepare you for what you need to know. It was a very low-stress training environment, and I really appreciated that.
Across the street from the UAL training center are the Radisson and Doubletree Hotels. I stayed in both and although it is a few extra bucks a night, I HIGHLY advise you to stay in the Doubletree. Both are crew hotels, but the DT is where SWA stays, is much nicer, and the staff there are wonderful compared to the RAD. Both properties are an easy walk across the street to several restuarants and the training center, so a car is not needed. You can probably Google "Stapleton Area", and see what all is around there. If you have any specific question, shoot me a PM and I'd be happy to answer them for you.
Best of luck,
CB