The answer to this question depends a little on what you're looking to achieve with a compression pedal--for instance, do you want that classic "chicken pickin'" sound on country records? Do you want that squishy-but-attack-y sound favored by funk guitarists? Are you looking to smooth out your playing and achieve sustain during leads like you hear on rock records from the 70s through today?
I know I'm in the minority here, but I highly favor the Boss CS-3 Compressor Sustainer. In fact, I rarely ever turn mine off, and my dream is to find a way to control it without having to stoop over--to the point where I've considered mounting the guts of the pedal in the body of my guitar.
Here's the thing: if nothing else, this pedal makes an EXCELLENT tone fattener. If you dial everything just a little past 12 o'clock, it just seems to expand the guitar sound tremendously. From there, I often tweak to achieve more sustain, or a quicker attack, or any of the sounds described above. I've even used the Level boost on tap in place of an overdrive pedal!
I'd suggest checking out the CS-3, if only because they are relatively inexpensive on the used market. It's definitely a pedal that requires a bit of time learning how to use it effectively, but once you start to get into it, like me, you'll probably rarely turn yours off.