So I'm running some demos of SSL-style bus compressors, and man, tough call! I figured the differences would be subtle at best, but I was surprised to find fairly noticeable differences among them.
 
I ran some drum/bass/electric guitar tracks into a submix then sent that into the various compressors, giving each the same settings (2:1 ratio, 30ms attack, auto release, set the threshold until I got about 2db of gain reduction) then level matched as best I could.
 
Man, I'm torn!
 
Cakewalk PC4K-S: sounds pretty good, although it doesn't seem to have as much character as most of the others.
NI Solid Bus Compressor: sounded pretty thin, actually.  (Strange, since I'm also trying out their VC76 and I'm really liking it)
Waves SSL Bus Compressor: punchy, little bit of midrange boost ("analog" button is on)
Cytomic The Glue: also quite punchy, seems to have a bigger low end
IK Multimedia Bus Compressor: again, punchy, and seems to boost the higher mids ("grit" button is on)
 
The Cake, Cytomic & IK have the HPF which is kinda neat, but the Waves really seems to have the best overall character, at least on this particular piece of music.
 
Figures, since that's by far the most expensive because apparently they don't sell it separately and must be purchased as part of the SSL 4000 bundle (which is currently on sale for $300 as opposed to the $750 price tag) or some of their other bundles, which are of course much more expensive.  The IK is $125 and Cytomic is $100.  And of course Cakewalk is free since I'm running SONAR Platinum. :)
 
By the way, I am looking for a "character" compressor, so while I could use Pro-C2 to do the job, it just doesn't have that "oomph" I'm looking for.
 
I guess right now I'd rank them as follows:
1. Waves
2. IK Multimedia
3. Cytomic
4. Cakewalk
5. Native Instruments
 
Any other recommendations I may have overlooked?

Have a look/listen...
 
http://www.bozdigitallabs...duct/manic-compressor/

I can't say I've tried all of those but I do have NI's Solid Bus Compressor and Cytomic's The Glue and I have to say The Glue just walks all over it. Amazing sounding compressor and not just on buses. It really helps when you enable oversampling on it though.

TDR Kotelnikov GE
Toneboosters Buscompressor
Pro-C
 

A few more SSL-style models worth trying, depending on your tastes, platform, aversion to iLok, etc.:
 
Slate VBC (specifically, FG-Grey) (needs iLok)
SSL Duende (needs iLok)
DCAM Buscomp
UAD SSL Bus Comp and Precision Buss Comp (need UAD DSP)
Nebula: AlexB 4KD G.Comp
 
And for grins, don't hesitate to grab the free Nomad Bus Driver, which is pretty wild but can work great in a lot of cases -- try it on drums, bass, keys, etc.
 
Cheers,
Eddie
 

+1 Glue here
 

i like and use the Waves C1 on my master buss.

No particular order:
 
IK Multimedia - Buss Compressor (Glue preset)
Waves - V-Comp
Waves - SSL G-Master Buss Compressor
 

I've really grown fond of the Slate Virtual Bus Compressors. I often use it on my percussion bus and again on the full mix down before final limiting. All three have their own characteristics, but you can load all three at once with the "rack" option and easily try them all out. 

I like Cytomic's The Glue, though lately, I've been replacing it occasionally with MJUC by Klanghelm. Often I will slap Slate's FG-MU ( or vari mu, can't remember) on the mix bus with no gain reduction because it gives a bit of a lift to the mids/upper mids area that I like on some things, especially rock stuff.