I have both an Ally and a Vortex. The Ally was great once I rooted it, put on a Custom Recovery, and installed Velocity 1.1. I liked the slide-out keyboard. The devs on the Ally forum did a fantastic job with the phone.
On the other hand, my Vortex was pretty much perfect out of the box for what I wanted it to do. It came with 2.2.2 on it. Once I rooted it and got rid of the VZW and Bing apps, that was all I felt inclined to do. AND, it's running Netflix which I could never do on the Ally. If it had the Ally's keyboard, it would be perfect for me.
It's all a question of personal preference. Obviously, for low budget phones, you can't expect Droid Incredible performance. And if you have no interest in rooting, the Vortex is likely a better choice for you, since the Ally is almost unusable out of the box.