I can't speak too much about sci-arc, but I'm very familiar with Pratt so can offer a little perspective on the program. 

In general pratt and sci arc seem to trade faculty back and forth a fair amount. Especially many of the more cutting edge practitioner/theorists who are in high demand and seem to hop around between these two schools and some others that also fall into the avant garde category like penn, though penn in some ways is still a bit stuck in heavy formalism. Pratt was actually in this exact same boat until recently, but the new chair of the department (came in at the beginning of this year) has been really shaking things up and bringing in some very interesting faculty. Pratt is moving quickly into the realm of object oriented ontology and non dynamical systems thinking in a pretty big way that sci arc seems to have been in for the last few years. The theory faculty at Pratt is top notch- between kwinter, leeser, ingraham and others there is a lot to explore. I'm happy to be finishing my degree but in some ways wish I was in your position because I think some very interesting things will be happening at Pratt over the next few years. In general Pratt is very disorganized, so be aware of that. As you mentioned, New York is really desireable. I've found over the course of my time here that Pratt has opened lots of doors into the professional world in the city that wouldn't have opened otherwise. If you aren't familiar with the emerging voices award series you should look it up- starchitects get all the hype but the firms who win this award tend to be some of the ones doing the best work in the US over a long period of time in a much more quiet way. Many of these firms (on the east coast at least) hire primarily from the ivies plus cooper union, pratt, and sci arc.