I started using Groove Agent 3 a few weeks ago and I am so excited with the results! It sounds very good and it's truly flexible.

It's almost like working with a drummer, to whom you'd say "I want a sparse beat in the intro, then a fill at the end, then a regular beat with hi-hi on the verse, then the same beat but with cymbals as well on the chorus" and so on.

Because it uses MIDI, it's fully tempo adjustable and you can also modify the beats. I find this much easier to use than WAV loops.