I voted RPG because they seem to be on top of that genre..... but I would say Platformers or Racers are their most produced.... they seem to have an stockpile of those type of games.
I think the PS2 facilitates RPGs a lot better, for a few reasons. The main one is that the PS1 and PS2 are pixel based rather that polygons, and for some reason the pixeled RPGs look a lot better to me that way.
The PS2 is home to a lot of awesome rpgs, so I went with that.
I mean just this year, they had Dragon Quest VIII, Magna Carta, Digital Devil Saga 1 & 2, Radiata Stories, Suikoden IV, and tons of others. Next year will be Kingdom Hearts 2 and FFXII.
And when you add all the awesome PS1 rpgs...well, there you go.
I personally think the RPG's are the best as well. PS2 has a long-standing line-up of RPG's. It continues sagas such as Final Fantasy, Xenosaga, Kingdom Hearts 2 is coming soon, Breath of Fire, and many others.