A list titles are those generally considered the best all-round pinball machines in terms of ranking (game-play, graphics, sound, artwork and anything else I haven't thought of) and consequently are usually high-priced as well. There is always some debate about which titles should be included in this list. Some people would rank A list titles simply on price as a measure of "collectability".
B list titles are very good titles but are considered not quite up to the standard of the A list titles.
In other words, it is the general opinion of the pinball community which determines a title's status. Some people choose to disagree with this general opinion.
