I had both as well and while I prefer the stage II, the stage I was awesome. I know they didn't revoice the tite gain mode but it doesn't sound the same on my ace as it did on the stage I deuce I had. It's very close, maybe it's a mental thing but I got a 'richer' tone out of it on the stage I.
Other than that, the clean is ridiculously good on both but I prefer the stage II's once again.. I typically prefer the tone of 6L6's for cleans but mesa pulled it off. Channel 1 is a launch pad for any pedal you want to throw at it, it does fuzzes amazingly well. Great for stomping on an overdrive for that nasty EL34 bliss and wild solos.
Fluid Drive is much better on the Stage II, I just have to say it. It can definetly be tuned properly on the stage I but I wasn't satisfied with that channel and the amp didn't wow me because of it.. plus I wanted to buy an Orange instead so I returned the stiletto
Bottom line, if you dig the tone of the stage I, snag it. The differences are a matter of taste.. and there are pluses and minuses to both. You can always sell it later if you play a stage II one day and like it better.