drglnc,
Seeing that most regulators breathe and operate very much alike and, for the most part, have no effect upon the other mechanical and physical aspects of the dive, I would recommend that you first buy your B/C/
Why?
The operation of your B/C plays a very significant part in your ability to master your buoyancy and control your ascents and descents. Becoming comfortable with your B/C and mastering its operation is extremely important to not only your enjoyment of your dives, but also your safety.
Another aspect of owning your own B/C is that should you start diving frequently, it will eliminate the issue of different weight requirements due to differences in buoyancy characteristics of different rental B/C's, which goes back to my previous observation.
Anyway, I'm sure you'll work out the best decision for your particular diving needs.
Safe dives . . .
. . . safer ascents!
the K