Well, as I've said in the past, I think going with a bunch of single IP lands could lead to problems in the future as it limits expansion but being so focused. Especially if a chosen IP falls out of favor -- not a big deal with a single ride, but when it's a whole land, I think there's the potential to look very dated in the future. I'd rather do a more generic Pixar Place with multiple franchises represented which would be better for expansion/replacements in the future. That said, it's the hot trend in theme parks these days (thanks, Harry Potter) so I can understand Disney's focus on it.
Regarding Monsters Inc versus Incredibles, I think the later is the more interesting IP to me and it would be cool to be the first park to have an attraction based on that franchise. But Monsters Inc is more conducive for a immersive themed land, in terms of the possibilities for food, merch and general atmosphere. There's specific places in that universe to use (MI factory, Monsters University [and Fear Tech], Harry Hausen's, Tony's Grossery. There's even a "Fine Art Gallery" shown in the first movie that would be a good location for merch.
I also think -- based on what I've seen -- that Monsters Inc sells more toys/merch overall than Incredibles [though they both would lag far far behind Toy Story and Cars] which might be a big motivating factor in any decision.