A lot of long, different answers, that if you go to page top to FIND,put in ribs,all forums,you may find some direction.
The Best of Ribs archives,give a lot of tips.
Smokin's ribs 101 will also give good guidance.
http://www.cookshack.com/index_guides.phpQuick thoughts are that those from a "used to be 225 lb,now more like 270 lb" market hog,are more likely to be a better product than a 700 lb-800 lb old sausage sow.
Previously frozen,often are harder to come tender,than fresh.
When you look at the slabs,some fat in them,as well as on them,are a good start.
After these,if there are specific questions,folks will jump in.
Hope this helps a little.