I write Phoenix mostly because that was the theory that was being taught at the school I attended back in the day. However, after hanging out on the (now gone) Phoenix Theory forum back then, I think I made the right decision.
Thankfully, I can also add non-Phoenix outlines to another dictionary that I always have running just for that sort of thing, so right now I have a few outlines from StenEd, Mark Kislingbury's StenoMaster theory, a few from his Magnum Steno theory, and several from other theories entirely.
As a "for instance," when I was attending my state's one remaining court reporting school, where StenEd was king, we had just practiced a jury charge drill, where the phrase, "preponderance of the evidence" came up a few times. I was taught to write that phrase like so: PRA*-UFDZ ... and I would mess that stroke up pretty much every time I tried to stroke it.
My instructor asked myself and my fellow Phoenix Theory students how we were stroking that phrase, and we all said the same outline. She then asked the StenEd folks what they were using, and they all said, "P-PD!"
Whoa! I quickly added an asterisk and stroked it to see if it would give me any issues, and then added that stroke into my "Glenz_Fast" dictionary.
That was a few years ago, and I can probably hit that original stroke (PRA*-UFDZ) with less issues than I had before, but I'm still going to keep P*-PD, just because.
--gdw