I don't see the point in using just one particular (OS X) operating system for penetration testing (and in general). It depends on the target/ assessment and sometimes what the client wants.
For example, if I have to reverse engineer something, I surely will use mostly Windows as for this platform most (and in my opinion the best) debuggers and disassemblers are available. I like linux too and use it often, but only to use it for everything just because I like it, would be stupid.
Limit oneself to only one operating system will not only limit your knowledge too but also the results you may got.