I hat to say this, because people tend to get in trouble for recommendind expensive equipment. However, the Avalon 737 is a great box for this kind of work. Especially if it is your primary work. The preamp is pretty decent, the EQ is awesome, and the compressor works well for vocals and bass. It will offer you an almost too smooth or too produced sound right out of the box in many cases. For voiceover work and especially narrative stuff, this seems like a real winning situation.
Now for more affordable stuff.... The RNC does a good job of transparent low ratio low gain reduction compression. Basically, just trimming the ends a hair. The DBX 166 and 1066 has a bit more of a "hairy" sound to it. Never really clean. If you use the overeasy, the compression is a little less noticable at the same GR values, and you tend to raise the threshold a little. Without the GR, its a bit more like a classic comp in its response, but its a more more drastic and noticable sound. The 160a is a nice compromise between the two. It seems to be a little cleaner than the others at higher GR levels, but still gets crazy on you (in a cool way) at higher ratios and lower thresholds
I would avoid the presonus comps, the ART's don't seem to work well to me. They look cool, they add a distinct and often cool character to the sound, but they do that it seems even when no compression is really triggered. I wouldn't even consider the Alesis, and the Behringer is actually an OK compressor. I still like the DBX's a bit more though. The compression on the Behringer is OK, but it seems that every signal run through ANY Behringer automatically gets a bit of a high and low pass to it, and the 3 to 12k region gets grainy and harsh. Not in a good way either