You do realize that it will not be possible to get into many of the bars and nightclubs in downtown philly until you’re 21?
Knowing this, most of the social activities at Penn will revolve around the undergrad greek life. Princeton has the same issue but instead of greek fraternities, people go to eating clubs on the weekends to socialize. There are a lot fewer bars/restaurants in Princeton. But if you are going to be stuck on campus for social activities anyway what difference does it matter?
I would classify Princeton as a discrete and charming small town rather than suburb. It’s about 1-1.5 hours from NYC by train. The area surrounding Princeton is pretty dense suburbs and the traffic can be a nightmare on Rte 1.
I guess it comes down to whether you want a city as a reality or a theoretical possibility. At Penn, it will be part of your daily life. At Princeton you will have more of a “bubble” experience (admittedly a very nice bubble) and would have to make the effort to enjoy the amenities of a major metropolitan area. Or if you want to take in the Greek scene, Rutgers is only 15 miles up the road.
Can’t speak to the academics as I didn’t attend either.
Actually you can get into bars and nightclubs in downtown philly and around Penn’s campus if you are under 21. First of all, many of the nightclubs have non-alcohol serving portions for people who are under 21 or wristbands for people over 21 for them to show at the Bar. And second of all, even without being 21… you can definitely get into many, many bars around campus and downtown. Of course I don’t personally have experience with that because clearly I would never try to circumvent the rules… 
buuuuuuuuut if you were interested in going to a bar or club before you’re 21, it’s most certainly easy to do.
And social life at any university should be about a lot more than parties and alcohol. It’s about art museums, concerts, music festivals like Made In America, restaurants, BYOs, poetry readings, street art, Pop Up parks and food trucks, and more. Every weekend is only a party if you make it one. Philly offers a lot of unique opportunities for those who enjoy the stimulation that urban life has to offer without ever being so large or overwhelming as to detract from the robust campus life that has a social scene only partly impacted by Greek Life. The debate team throws parties in off campus houses and the boys in KSig do philanthropy in the center of College Green-- your social life is what you make of it at any institution you attend. It’s about having opportunities readily available to you that fit your interests and then taking advantage of them without losing focus on your academics.
Princeton smells a lot better than Philadelphia.
" Plus, i have relatives who used to live in Philly and tell me its an amazing city. Will i , as a penn SEAS student, be able to take out time to just visit and explore the city once a week? "
I was Penn SEAS, and I had no problem going to parties during the week and going to South Street on the weekend.
As for the smell, Princeton smells pretty bad too, all those noses in the air can’t tell maybe?
I think you need to consider greatly the difference between what is immediately around Penn, not just in Center City and South Street, vs. what is immediately around Princeton. As a NJ native, I do not feel that the vibe around Princeton is in any way like a college town. Penn has many small businesses such as shops and restaurants in the immediate (as in within 3 blocks of campus) area. It will be clear where you can easily go, and where you should stay away from in the immediate area.
I guess my point is, at Penn you don’t have to be limited to only on campus, whereas Princeton has much more of that vibe - what you get it only directly on campus unless you have a car. Yes, you could go to NYC or Philly, but the time and trouble to do that is much more than going to Center City or South Street from Penn.
However - if you are married to the idea of an aerospace degree, you may want to look at schools that actually have one. Not that they haven’t had students doing aerospace research, but you would be an exception.
USN&WR doesn’t have Princeton in the top 10 for aerospace engineering:
http://grad-schools.usnews.rankingsandreviews.com/best-graduate-schools/top-engineering-schools/aerospace-rankings
but then I did check, and they are #11. So the top ten might be good places to start looking.
Cornell, UMDCP, and Virginia Tech are all tied with Princeton at #11. Penn State is #16. RPI is #22; my son is there and got pretty good merit aid based on his SAT scores (not wonderful, but I hope your test scores are better).
Princeton is ranked #7 in the US News ranking of undergraduate aerospace programs (probably more relevant than graduate programs listed above)
http://colleges.usnews.rankingsandreviews.com/best-colleges/rankings/engineering-doctorate-aerospace-aeronautical-astronautical/data
Penn does not appear to have a program.
So if the OP wants to pursue an interest an aerospace engineering, then Princeton would be a better choice. However, students frequently change their minds about majors, so this might not be a determining or even that important a factor for the OP.
I am an old fart, but I chose Princeton because it was in a bubble. I am a woman, and wanted a place I could walk around in at night and feel safe, and I was poor, so I couldn’t afford to go out in the city, any city, on weekends. I wanted a quiet, more bucolic setting where students made their own fun and activities.
You can go into the nearby cities from Princeton, but we were too busy and I was too poor to do it very often. This was back when NYC was dangerous and scary, too, fwiw. I can remember riding the bus in and witnessing a knife fight as soon as I got off.
My own kids went to college with more ability to spend money. One is in a more urban environment and likes it, the other chose an isolated school, much to my surprise.
Son sophomore now, he chose a more relaxed suburban setting too. On the flip side, he is so busy studying, playing, going to the gym and in clubs, how important is the surrounding area? He has almost no free time. I think last year he left campus once to see a game. For him it is clearly a bubble, but a happy and exciting one.