Quality of aftermarket iPhone screens?

Generally speaking, the higher the price the better the quality. For a quality screen, you are looking for two major points:

1. The screen is listed as OEM or original quality LCD (which iFixit parts are)
2. They offer a significant warranty on the part of 90 days or greater (some places offer lifetime)

You can get cheaper screens and install them. The biggest difference will be screen reliability, strength against future drops, and quality of LCD color and touch sensitivity.