I had a nightmare weekend with everything about our move from apartment to house going wrong, so I'm a little late chiming in, but here goes.
Ascend: For the price and overall performance, you really can't beat it. As an entry-level Android phone that you don't have to commit to a 2 year contract AND pay 200 dollars for, this may be the best choice on the market. With rebates, you can get this for 100 dollars on average, and there is already a custom ROM out there, as well as others under development, including at least a couple that are supposed to be running Android 2.2 OS.
Specs: 3.5" touchscreen, 528Mhz stock processor, 256MB RAM, external SD card up to 16GB supported.
Caveat: No discrete graphics processor, 2.1 OS. No standalone GPU means poor performance on graphically intense games. Angry Birds is a common complaint on this phone, including multiple button presses just to get it to load and display properly, and the framerate will frustrate you a fair amount of the time. 2.1 OS means you do not have the stock ability to install apps to the SD card - they instead install to internal memory, which is not much on this phone, and you will quickly get low memory warnings, curbing your app-downloading binges severely.
The Icarus MOD for the Ascend remedies the apps to SD card issue, and I must say it is worth the time and effort for that feature alone. It also removes preloaded "bloatware" apps that are packaged in by the carrier, and runs significantly faster than the stock installation.
LG Optimus variants: Pretty much every carrier has a version of this phone, the names differentiated by the letter at the end, such as MetroPCS with the Optimus M, or Virgin Mobile with the Optimus V. This phone is stronger than the Ascend, but also carries a roughly $50 premium on price, averaging $149 with rebates. I have personally played with a Sprint version of this phone, which a coworker of mine has, and it is definitely snappier performance-wise than the Ascend.
Specs: 3.2" touchscreen, 600Mhz stock processor, 512MB RAM, standalone GPU, Android 2.2 OS, up to 32GB external SD card supported.
Caveat: This phone, in every variant I've seen, does not have a physical End Call button. This means you will have to wake the screen again to press End. It has a slightly smaller screen than the Ascend, although both run at 320x480 resolution, and the quality is comparable based on what I've seen.
In my objective opinion, the Optimus is definitely going to be a stronger performer overall, with double the RAM and a standalone GPU. My coworker's Optimus made my Ascend feel slow, even with Icarus installed on it. I don't know what benchmarks between the two would look like, but based on my experience, it has to be at least a reasonable gap. If you need to get out with the least money possible, and playing higher end games/running lots of apps isn't something you'll likely be doing, then I recommend the Ascend. If you have the extra money and you want overall better performance, then I would have to recommend the Optimus. All things considered, had I done a little bit more research and known a couple more things, I would have gone with the Optimus M, being on MetroPCS, but part of that is because I am used to quickly testing the limits of a new toy. The other part of that is, I never owned a smartphone prior to the Ascend, and after finding out all the wonderful things I can do with it, and seeing where it fails, I personally want more. your mileage may vary.