Hand's down, Sheraton Suites! In my experience, the Westin doesn't even come CLOSE to the SS, and that's even considering that I was u/g to a large suite at the Westin. The SS is considerably newer, the rooms are just great (plus I like the 'separate bedroom' layout), nice gym & pool, the Club Lounge is awesome, but the hotel's real strength is it's staff. Without exception (at least in my experience) they are the most helpful, cheerful, efficient and welcoming I've encountered anywhere. They really do bend over backwards to ensure you have an excellent stay. I travel to Edmonton frequently, and I like the SS so much I'm considering spending at least the 1st and last night of my trips in Calgary at the SS, even with the drive.
Only downside is they are usually more expensive than the Westin. But it's worth it!