It depends on which Phase 90 you're talking about. The newer phase 90s I think sound more sterile and have a more upper midrange thing going on which can be unpleasant when combined with distortion.
The older script phase 90 sounds great, it's a little more subtle phase then the small stone is with it's depth switch engaged, but the small stone can get a more bubbly type of sound.
I personally prefer the phase 90 for subtle phasing, and I use my Pigtronix phaser if I want a thicker phase, or a univibe sound.
Plus my small stone has horrible reliability issues, the switch breaks in it all the time so I never put it on my board, I just use it for recording.
And I don't actually own a phase 90 but a Retro Sonic Phaser which is a script logo Phase 90 that lets you adjust Depth and Intensity as opposed to just rate.
