Michelle Dozois (Peak 10), Patrick Goudeau (MWT workouts), Bob Harper (Inside Out Series), Susan Chung, Toby Massenburg, Kelly Coffey-Meyer, Jari Love, Shaun T's Insanity, Chalene Johnson's TurboFire and Chalean Xtreme, Ilaria Montagnani, Amy Dixon's Breathless Body workouts and just about anything Jillian Michaels. They all feature regularly in my rotations. But Cathe is always featured most; she's my #1 favorite.
Right now I am doing Body Beast and I like Sagi, but I'm not sure he is or ever will be a favorite trainer. But I do enjoy the workouts. That's actually how I feel about Shaun T and Chalene--I love the workouts of theirs I already own, but I'm not always motivated to purchase their newest workouts. But that could be because everything they do is in a "system" rather than individual workouts.
Some that I mentioned are always autobuys like Cathe--anything Michelle Dozois does in her Peak 10 series, Susan Chung's Rapid Fire workouts, Toby Massenburg, KCM, Jari Love. Most Ilaria Montagnani workouts (especially Atletica workouts) and any Amy Dixon Breathless Body workout. Jillian Michaels is also almost always an autobuy, too. I actually love her workouts, they just don't seem to fit into the rotations I create very well. I usually use her 30 minute workouts as doubles workouts--but my favorites are her Shed & Shred and Hardbody. I love those workouts.