Mike et al,
When I buzz my mouthpiece I normally try to get a really clear buzz at about a mp level.  If we practice buzzing much louder, the buzz covers up the air to the point we don't realize how inefficient we are.  Once I plug this buzz into the trumpet, I can decide if I like the sound or not.  On Bb, the clearer the buzz, the more I like my sound, but I play a 72 bell >Bach. On my C, this same approach projects really well, but can sometimes be a little callous sounding for lyrical playing, so I might let a little air into the buzz, which is pretty easy to do.  In general, the higher the pitch trumpet, the less perfect a buzz I feel I can get away with.  On cornet and flugel, we can get away with almost anything, but I still prefer the core to the sound that comes from a pretty clear mouthpiece buzz. Admittedly, this concept probably favors "legit" playing, but I use it for everything.  The easiest way to get a grip on this is to trade phrases with ourselves, alternating between the trumpet and the mouthpiece, trying to do exactly the same thing twice, then experiment with the quality of the buzz.

A couple of other important points:
1.  It can take a good player a few weeks of hard work to really consistently buzz easily and efficiently if they haven't done it before.
2.  Everyday once your best mouthpiece buzz is established, put the horn up to the mouthpiece while it is still being buzzed just to check and see if you need to make a slight adjustment in horn angle.  It is amazing how often this is the case and how rarely anyone thinks of it.  Ghitalla was the first to point this out to me.

Thanks for asking, Mike, you made me feel useful today!
John Daniel
Prof. of trpt
Penn State Univ