I have some favorites, and here's the what and why for me
1-SMACK!_this is Avid's version of an LA-2A and it works really well on voices
2-BF76- works well on acoustic guitars and I also use it before SMACK! on vocal tracks
3-Slate's Distressor(with Slate's Neve EQ in VMR) is great on a drum compression bus. The Distressor allows for adding a distortion element and the EQ is good for gentle added low-end punch, or a slight dip around 500Hz.
4-Waves Puigchild(Fairchild) has some nice character for electric guitars when needed.
R-Comp is very popular, but I just find myself using the above. The only other "2 cents" I have is to avoid the stock Avid Dyn3. In critical listening, it caused some distortion that was not pleasant at all.
