Even though other daws handle .acd and or rex loops I have always thought the GUI was especially easy to use in Acid Pro. Easier than in the others. Couldn't be easier. In addition, The loops were some of the best to get a pop or rock tune started. I hate to say it, but the loops in CW I never had any use for.
In Acid you had easy access to bass, drums, guitar hooks whatever. Most of it fit very well with what I was doing at the time. IMHO probably the best daw for turning out fast quality ideas on the fly.
They were one of the first to do it. They developed the acid system and to this day it's one of the very best there is.