TravelCodex has published a thorough listing of the kinds of aircraft that American Airlines flies, and how much comfort (or discomfort) to expect in each.
The blog post is here.
If you fly American (as I often do), this listing will tell you what seat pitch (distance between rows) and seat width to expect in First, Business, Premium Economy, Main Cabin Extra and Main Cabin seats. It also includes information about IFE (in-flight entertainment) and power available at seats.
This is an excellent resource by Rohan Anand, well worth bookmarking.