Another post on the top ten troll questions.
(3). Ascending or descending armor class?
Descending, definitely. I've talked a lot about this, about how ascending AC systems tend to treat AC more as a number, with the implication that there is no upper limit to that number. Also, I have some tricks based on the supposition that armor class is descending, which wouldn't work if I switched to ascending AC. In other words, ascending AC is vastly inconvenient for me. That's fine, because Target 20 actually eliminates the need to switch to the d20 SRD standard method; it gives you the exact same benefits, with descending AC, as the d20 system does, with ascending AC. I already have the descending armor types memorized, and they work with Target 20. I have the option of going with what's easy, or going the more difficult route of memorizing ascending AC types (or converting every AC as I encounter it.) A whole lot of work for no extra benefit.
For people who started with ascending AC, the situation is reversed. Why should they switch to descending AC, even to use Target 20, when that will mean memorizing which types of armor match up with which AC?
It doesn't matter how "logical" a method is. Sometimes, it creates a cascade of other problems for players used to doing things a particular way. If you know something backwards and forwards, you'd be a fool to switch to a new method.