I stayed at both several times in 2016. I personally prefer the Regency and consider it the best downtown Denver hotel not named Four Seasons or Ritz. It's a newer property than the Grand and I've personally found the service to be much better. At the Grand, I felt the front desk staff were often inexperienced (long check-in times, key not coded for Lounge floor etc). The gym is much better at the Regency if that's a consideration, although the pool is better at the Grand.

I've never used a DSU, but have received comp upgrades at both. The Grand was fine. Again, I found the Regency better but I may have received a suite that was better than what a DSU would provide.

I found the lounges to be fairly similar in offerings and service level.