I too stopped at a VZW store to look at the Ally. It was sitting side by side with a Droid so I was able to play with both of them at the same time. In all honesty, i'd have to say the performance was just about equal on both units for what I tried. Can't really say how downloaded apps or games will perform on one vs. the other because all they had was the stock apps running. I did notice a bit of lag at times on the Ally when pressing the Home, Return, etc. buttons. Nothing drastic, but I did have to press the home boutton twice a couple of times on the Ally to get it back to the Home screen. Not something that was a deal killer for me though.
I found the keyboard was nicer to use on the Ally because the keys were not flat, but I didn't have trouble typing on either of them. I did like that the Ally had phyiscal Call and End buttons.
As for looks, again I liked the Ally because it had more rounded edges instead of that rectangle look the Droid has. While it was still very boring looking, it was at least a little bit more asthetically pleasing to look at. The Ally is also a very sturdy feeling phone like the Droid is. I felt like if I dropped it, the case alone would protect it from damage just like the Droid case feels.
Both displays were very crisp and clean and reading text on both of them was very easy. I'd say the Ally looked a little brighter, but that may have been due to the way the VZW reps had the display settings setup on each one. Maybe they had the Droid brightness turned down.
Couldn't test the cameras because of the antitheft attachment on the back of each, but just looking at the specs, it would seem the Droid should take better pictures in theory.
In all honesty, to me they are basically the exact same phones. Not being an expert on these phones, i'm sure there are some subtle differences to the hardware (like the bigger SD card that comes stock on the Droid) that would make one better than the other, but to the average user they are probably interchangable. Myself, i'm going to pay close attention to some reviews to see if there is anything drastically better on the Droid that would make me pass on the Ally. If not, I may end up getting the Ally because I like how it looks better than the Droid.