I suppose when deciding on a build you should read some reviews, try out some in shops, and match your needs and expectations to a pedal. That way you're ound to get close to what you want on the first try.
For me there are kinda 2 types of compression.
First is one thats very sustained, very "squishy", and fattens up the tone i.e. dims the highs and adds balls (not really an expectation from compression I know but useful none the less). It has a pronounced sonic "effect", like the Dyna sound byte on the dunlop site. Personally I associate these squished sounds best clean/jangly tones and chording. If used on a high gain pedal/am channel, I find it cuts too much out of the sound as others have stated.
If this is what your after, I would go for a Dynacomp, Ross or Orange Squeezer.
The other compression I use is more for "feel" than sound if that makes any sense. (Alike many others) I have a comp on all the time. Sustain is set very low - just so you can barely hear the "wall" kick in when you really attack the strings (apologies - cant think how to describe it but hopefully you know what I mean). Volume I set just above unity. I find it evens out the sound and balances out the difference in string volumes etc, especially when I switch from pick to fingers and am playing on the higher strings/higher registers. Im not sure compressors are design to balance out levels across the strings, but it works for me!! These "transparent" compressors translate to distorted and clean base sounds.
For these senarios I would go with a Compulator, Philsophers Stone, Ibanez CP9, Boss CS2/3 or Marshall ED-1 (I hear these are pretty good provided you get one which will last).
My personal favorite is a DOD Milk Box. Its not an popular choice but they are FANTASTIC boxes. You can still buy the odd one for Ģ50. Not sure they still make them.
I believe it shares the same typology as the CS2, CP9 (therefore Ross/Dyna to some extent), however, it covers a lot of ground. It can do the transparent thing, and the effected squishy sounds also. I've also had recent success with a Compulator clone built from a project at _______________. This is great great great natrual sounding and versatile optical compressor.
My $0.02, or pence as im in UK.