If I am to have one pedal for the bass, it is EQ, but compressor is certainly the second one. I used to have a compressor from the cheaper end of the price range. Buying cheap gear always backfires. The bass sounded better without the cheap compressor than with it. Hence, I searched the wonderful land of Internet for a good compressor. There were lots of positive reviews about MXR M87 and the fact it is not to be found second hand says a lot. I bought an M87. It rocks and funks and whatnot.
I am a simple guy, so my usage of the product is simple. The compressor is always on with rather mild ratio and attack. The sound guys on the gigs are always happy with the sound that is coming from the stage. The compressor is one of the reasons behind that.
Once, I was ignorant and not understanding and I thought that I need to learn slap bass. Even a beginner sounded like a decent slap bass player with M87 with fast attack.
This is probably not the best bass compressor known to man, but you do not need a better one. Trust me.