I continue to use both processors, and I agree that each has its place. Breakaway is incredibly clean and easy to use, and its latency can be brought to a point where I can easily put it anywhere but where a live DJ might use it in his/her headphones. Today, that isn't much of a problem, since the vast majority of stations in my area use some form of digital transport between studio and transmitter. For me, you could have several minutes of latency and I'd have no reason to care.
Stereo Tool allows for the "tinkering" that Leif chose not to allow in Breakaway. For those with an understanding of how these things work, ST might be their choice. The program has also progressed beyond where Leif locked his down, so there are features that have continued to develop. That BBP still compares as favorably as it does is, I think, a testament to the quality of Leif's work.