The Marriott City Center is a straight shot down California to the Convention Center. I loved my little room with a fluffy king-sized bed, dressed with down pillows, my favorite.
There was no charge for 800 # calls (a personal perk I love, so I can avoid charges for using my modem). I ordered room service. It was very fast and courteous. The French onion soup with topped with pepper jack cheese was awesome.
I would choose this place for sure next time I'm in Denver for a big convention!