Triplet/ED/fuorite APO

Is there a clear progression of APO designs? I've read about triplets of standard, ED and fluorite "glass", and of doublets made from fluorite and ED glass. I assume all APO's are not created equal but is there a clear heirachy?

Then there are Super APO's, quad lenses, and TOA... just a little confusing.
-Guy

Guy,

If I may pass along some good advice given to me (repeatedly) over the past several years: If you are not already in an astronomy club, join one. Attend star parties. Take every opportunity to look through these scopes yourself. Larger star parties will give you the opportunity to look through a variety of apo configurations made by different manufacturers. These are generally very expensive scopes for their aperture so seeing for yourself is the only way to decide if one is right for you.

Good luck,
Milt