Maybe its because music and voice to me is the most important aspect. I really like Sara Ramirez' voice, but thats about it. DRS has a really good mix of singers, from the high belters to the soft crooners. And although the shows both have clever lyrics, I think DRS is funnier in a not so "in your face funny" like Spamalot...
DRS has a plot and Spamalot doesn't. DRS has songs that relate to the plot and Spamalot doesn't. DRS songs and dialogue have jokes that relate to the plot and Spamalot doesn't. DRS was robbed a Tony and Spamalot wasn't Spamalot is crap and DRS isn't.
Sorry if that was mean, it's just my opinion. I really don't care for Spamalot much. The movie was better.