Having stayed at the Adlon and Hotel de Rome, I still prefer the Regent. I find the Adlon to be crowded and the service to be ok at best. While I always stay at Villa Kennedy in Frankfurt, and think that it is without doubt the best hotel in
FRA, I found the HdR not to be a great hotel for business travel.
On the other hand, I have stayed at the Regent many, many times, and have not found the service to be lacking in any way, and the rooms are large, comfortable, and have a good desk for working.