We actually decided to try out a character specifically optimized for social interaction in general, and debate in particular. And ... we came to the conclusion that the debate rules are nice, but a bit shallow -- definitely less deep than certamen ones (see below). Also, they tend to favour focusing on some Abilities, and disregarding others such as bargain and etiquette -- which should instead be crucial for debate. From a strategic point of view, it's nice how debates interact with certamen: you can win a debate, but certamen has the final word; then again, if using debate you manage to convince all the archmages that it's in their best interest to champion your cause in certamen...
Focusing solely on the HoH:S debate mechanics, we came to the following conclusions:
a) a character optimized for debate can usually soundly defeat someone who is not.
b) unfortunately, the more optimized the character, the shallower the "gamist" experience: that's because, while you do get a bonus when choosing the "correct" Ability combination against an opponent, in the long term it pays off to specialize in one attack ability (and raise to decent levels one defense ability) and just pound on with that, whether it's the "right" ability or not. Not only do you get to concentrate your xps, but you can also focus your virtues (Puissant, Affinity etc.) on that single ability.
c) for a debate specialist, it pays off to be better at attack than at defense -- because most of your opponents will be weaker than you, and whether you successfully defend against them with a large or with a small margin makes no difference, but the greater your attack margin, the greater your victory margin. That's not quite so true if you regularly face other debate specialists...
d) in my opinion, Intrigue is probably the best attack ability to focus on, because it's such a versatile ability anyways for a socially-oriented character. Artes Liberales is a close second (and possibly the best for a magus) because 1) it's an Ability for which there are lots of books, 2) it helps with a lot e.g. with ritual magic, horoscopes etc. 3) it's strongest against Leadership, and your magi opponents are likely to have spent more xps in Leadership than Charm or Guile (the other defense abilities).
e) in my opinion, for the same reasons Charm (which is strongest against Artes Liberales) is probably the best defense for a debate specialist to focus on, particularly against magi, and it's a nice "all-around" social ability to have.
I think a much more interesting set of debate rules are the ones that Atlas makes freely available on their website, adapted from they Dynasties and Demagogues game (which in fact predate the rules in societates). They involve 24 different "maneuvers" -- stuff like "the big lie", "humorous jab" or "hint at consequences" that are really full of colour and offer challenging mechanics.