For mine, the factions that most usually morph into superpowers in AI hands are Spain and Sicily - and I always just figured that was down to favourable economic conditions.

The Byz and the Horde will both start strong but collapse...I don't know that I have ever seen either of these runners stay the course, so the key here is just to survive the initial onslaught.

The wild cards are definitely the Eggies and the Danes. When the AI gets these two cranking, it can be a steamroller all right!

My current XL campain as Serbia had an unusual twist - Spain was pretty dominant, then suddenly disappeared when the king died without an heir, leaving the balance of power poised between Sicily (controlling virtually the whole mediterranean, all of northern Africa, and most of the Middle East, and most of Britain, Serbia (me) with central europe and Iberia, and Denmark with most of Scandinavia and northern Europe, together with an ever increasing share of Eastern Europe (they are smashing the Horde).

The thing that intrigues me about AI superpowers is the huge numbers of troops that the AI maintains. Interestingly when I look at what they have in the above example, the Danes seem to be using almost all home grown types, whereas the Sicilians seem to have heaps of "bribed" troops from other factions on the roster....maybe Sicilian style, they "made them an offer that they couldn't refuse"....