BlackAlbino

To be perfectly honest, I don't think that you can lose either way. Relative to each other, I would say that Yale's advantage is that it has New Haven (a city with *tons* of stuff to do, much of it free to us as Yalies)... Princeton's advantage is that it is not in New Haven (a city in which the issues of American poverty are front-and-center, although more exaggerated in terms of the "danger" factor than the media would have one think)... I do think that you are right about only having access to a single college, but somehow one of the graduate students here has access to all of the residential colleges... and in terms of hanging out in wonderful garden spaces, there are a few times when I've just lurked around the entrance for a moment or two until a student goes in/comes out and then enjoy the gardens... there are also events that happen in the residential colleges (I belong to a weekly lunch colloquium) and we still have to wait for undergrads to let us in (and this lunch series typically involves around 20 faculty and another two dozen or so graduate students!!)... it hasn't been much of a barrier to my enjoyment of things here so far!
 
In any event, Princeton is darned amazing and is easily my favorite Ivy campus... Best of luck to you in choosing -- that is going to be a tough choice!

I  can't speak to the specifics of the dining plan, but a few of my friends lived in HGS for their first year and didn't care for it. The building hasn't been renovated since the 1930s if that serves as any sort of indicator. I'd at least consider looking around Wooster Square and East Rock as well. I live on the very far north end of East Rock and it is a 30 minute walk or 10 minute bus ride (free Yale shuttle that comes every 15 minutes or so during the semester). On the end of East Rock where most of my colleagues live, it is more like ten minutes. That's not to suggest that HGS won't be exactly what your looking for, but I haven't met anyone who thought that was a very great place to live -- and the meal plan is definitely pretty spendy!

Be aware that at Yale, there are opportunities for graduate students to become "liaisons" of sorts with undergraduate colleges, which comes with the privilege of access to undergraduate colleges, facilities, and an opportunity to intermingle with them. I have a friend who has done this for two years in a row and has met some wonderful people. She also gets two free meals a week in the undergraduate dining halls (which are quite good, actually, as is the graduate hall in HGS). In return, she hosts one event per semester in the college around a quasi-academic (or just plain fun) theme... it isn't odious and it is meant to provide graduate students with an opportunity to mentor undergraduates, interact with them, etc. I am not aware that it is particularly competitive to get one of these positions either.
 
In any event, as a current Yale Ph.D. student, most of my classes have at least two junior or senior undergraduate students in them and they certainly don't behave differently and nor do the professors or other students interact with them differently. 
 
In short, I don't know what your field is, but in my field (history), the divide is as big as you want it to be, essentially.
 
Sorry about the brief Yale interlude -- back to all things Princeton.

You can find it here.  Questions, comments, and suggestions are welcome!  I am curious to hear what you guys find interesting, as this will help determine the content of future posts.

I think this is what you are looking for:

http://pubs.acs.org/cen/education/8139/8139education1.html