Just try whatever you can get your hands on, but keep your settings pretty tame. The attack is usually kept pretty low on bass, but if you find you need more attack, you can open it up. The release is wherever it sounds the most natural to you. If the threshold is low, the ratio needs to be low as well so you don't squash everything.
For natural-sounding dynamics control, I really like the ReaLimit. You can see which peaks are being cut off, and the visual representation allows me to identify problem areas so that I can delete problem spots like the hits I do in time with the snare that sound like electrical shorts, or use volume automation to keep them under control. It doesn't give you a compressed sound per se, but it really helps keep the dynamics under control in the simplest and most intuitive way possible.
For a long time, I was a preset guy w/regard to compression, If you're using the Reaper bass presets, you never want driving rock bass, no matter how driving or rockish the sound you're looking for. It's overcompressed and murky. You always want the other one, and it usually sounds good. Sometimes you have to lower the threshold a bit for it to engage. Then you can mess with the controls if you want to.
My favorite bass compressors are the Waves R-Bass and the Waves SSL-E channel strip. I use them because I have them, but I never recommend spending money on fake hardware plugins that Analog Obsession makes for free, and I frequently use random free fake hardware to compress bass. And while we're talking freeware, Melda's freeware package is fantastic. Just download the whole thing. You never know what you're going to use, and their graphics and interfaces are the most intuitive around.
My secret weapon is the Klanghelm IVGA saturator, which is free. It puts some grind into your bass sound that will help it be heard. Mess with the settings, but don't be too critical until you hear it in the mix.
