Early on, my favorite tracking compressor was the LA-3A. You could use them on anything. I still use hardware compression when recording most individual tracks, even in the box, kind of a holdover from my tape machine days. I usually run the kick and the snare through the compressors in the Porticos, but not a lot unless there is an effect I’m going for. My current vocal favorite is an M 149 into the Avalon with a little compression, then through an 1176 with a little more and then to the converters for recording. Our engineer Jake Saghi came up with this chain for a Matt New single in part through a shoot-out process, and I really like it.
Compressors can also help groups of instruments or vocalists hang together, so I often use them on those busses when mixing. It’s one reason I use busses rather than VCAs in Pro Tools. Another trick that digital has made easier, and less expensive, is chaining compressors in series so you don't ask for too much out of each one. This is cheaper and easier in mixing than going out to the hardware that we use for recording.
Compression on the mix bus is a whole different matter, and I’m experimenting with new ways to do that. In the past, I almost always had 1176LNs in there, with just a few db of reduction, 4:1 ratio, attack and release adjusted by ear. Rather than mix bus plugins, I now use almost exclusively the Rupert Neve Master Buss Processor. It's a hardware device that's an extraordinarily flexible mastering instrument. Transformers, red and blue silk, texture, width, depth, compressor and limiter. Ya gotta love it. Then a little touch of Ryan Schwabe's Gold Clip.
As everybody knows, many engineers have been disturbed by the trend to squeeze the life out of pop music in mastering, and even in mixing, to make it sound loud. Today there are brick wall limiter plugins with built-in loudness metering. You can stomp that tune right on down, make it loud and irritating. We do usually have a lookahead brick wall at something like -0.2 dbfs after the MBP and Gold Clipjust as a final insurance clip catcher. I'll sometimes crank that up on client mixes so they can get an idea of the finished product. We have a calibrated hardware spectrum analyzer and loudness meter on the control room monitor feed. At the end of the day though, for mastering, the best move is to hire a pro and send them a mix with dynamic range to work with. I try to send the mastering engineers tracks in the 10-15 LUFS range to work with.