There's an excellent web page that reviews almost every compressor rack or stomp unit known to mankind, and it's a good read if you have the time to wade through it:
www.ovnilab.com You may want to start with their TOP PICKS:
http://www.ovnilab.com/reviews/toppicks.shtml
Personally, I've mostly used rack units for bass compression:
dbx 160x
dbx 163x (one knob squeezer)
Empirical Labs EL8 Distressor (this compressor has spoiled me for almost anything else other than studio grade high end comps)
Currently, I have dabbled with the TC Electronic SpectraComp, which is IMHO a neat little $99 pedal, but a quirky beast for sure. Some bassists have had great luck with it by selecting a TonePrint they like and keeping it really simple via the one-knob operation. Others, like myself, have been fascinated by the fact that it's a true 3 band (lo/mid/hi) multi-band compressor, fully editable and programmable via software, with a TON of available parameters, 3 of which are assignable to the hardware knob on the device. Simple, yet very complex. Quirky.
If you're looking for a compressor to simply lop off some of the jagged edges of the bass sound (IOW, mild compression), then you probably can make most anything work, with a few exceptions, of course. Your style of playing and the even-ness of tone you produce on your instrument also has a lot to do with how much compression you really need.
Personally, my playing style and preferences are specific and perhaps demanding, looking for more than just simple broadband compression. As mentioned above, for years I used the EL8 Distressor, and chose to solve the problems I had by throwing money at it with a studio grade compressor, and yes, it worked GREAT for me. Loved it.
For bass in particular, I tend to favor a pedal compressor that has one or both of the following features:
- parallel blending (aka wet/dry mix, to help preserve low end and dynamics with higher levels of compression)
- multiband compression (literally, a separate compressor for each tone region, at minimum a low and a high band)
Hope this helps.