I use both - Tend to favour ST1 V2.5 though.
Plus/minus on both.
ST1 better for me when composing on the fly while looping,
VST Synths stay in sync, after two or three passes in X2A they are all over the place.
Chase MIDI notes i like in ST1, along with Folders into busses.
Even though Staff view in X2A is not that great, i still use it for some Orchestral stuff,
then export MIDI/Audio into ST1.
No staff view in ST1 [and no plans for it at the moment]
I get odd things happen in Pro channel and strange goings on elsewhere with some hangs.
[I have not got to the bottom of them]
I don't get hangs or crashes in ST1.
Horses and all that, i suppose i like them both for different reasons.
Between them both i get plenty done, and that's all that matters.
Garry