Opto for bass, though Logic's "Opto" circuit doesn't work anything a real opto. Try the Waves Renaissance Compressor in opto mode instead, it's got fast release during lots of GR and slow release with small amounts of GR. It's great for getting punch and controlling flabby tails.
The Electro mode in Waves R-Comp is great for low level compression since it "caps" the total amount of GR and reverses the behavior of the release compared to opto, i.e. slow release with lots of GR and fast release with small amounts of GR. Great for pulling up details in vocals, etc.
On vocals I often use an 1176 which is a FET compressor/limiter. It's quite organic and changes the frequencies in the signal when pressed hard. It's also great for fattening snare drums and extending tails.
On the mix bus I sometimes use the SSL G-series compressor (hardware), which is a VCA compressor. Simple, clean and bouncy with a nice full auto-release.
For mastering I also use a Crane Song STC-8/M which is a Class A compressor with an optional auto-release that mimicks traditional opto characteristics.
Currently working on Vinnie Who (EMI), Alphabeat (Universal), Nik & Jay (EMI), Infernal (Border Breakers), Sisse Marie feat. Yes-R (Universal), Clemens (Universal), Ida Corr feat. Fatman Scoop (Lifted Housed)