After using all four, I've found to rank them (for myself) in this order, Omni, Monocomp, Apex, Monocle - I can get the Omni to pretty much act like any of the other 3, only a tiny bit of the monocomp is untouchable, with my setup at least. It still has a color that nothing else I have can do.
I'm also not a compressor guy, but the 76CB is my second favorite to the O M N I.
I rank them, Omnicomp, Monocomp, Cali. Totally agree with @labeledbass regarding the versatility of the Omnicomp. I view the Apex as being completely different and un-rankable... suffice it to say that it will never leave the front end of my board, and it will never be turned off. The Apex is the king of whatever it is.