Glasgow or Aberdeen which one is the best ( studies, campus, people)?

Depends on your expectations. Aberdeen is excellent, if you want to take the oil & gas program, it is worldwide renowned.
Otherwise you should decide which city fits you best.

Glasgow is a big city (for Scotland) with a lot of urban culture, clubs, pubs and so on - including also all the typical problems of students living in a big city. Difficult flat situation, dirty, noisy, no parking space and usually more rain than on the east coast.

Aberdeen is a much smaller city, directly at the east coast. They have a nice student village located nearly directly at the coastline. You're able to go for a run in the morning, see some seals and sometimes dolphins. Because its located on the east coast, Aberdeen has not as much rain as Glasgow, but the amount of rain is still annoying (it's still Scotland). There is a nice new student gym and a new library, with fantastic views over the Aberdeen bay. However the cultural activities are kind of weak and the city is simply ugly (grey & noisy). There are a few pubs and clubs and you are able to party if you want to - however during the summer vacations they're almost empty - because the domestic students, and also a lot of foreigners travel home during summer vacation (June - September). This time can be exceptionally boring.

To sum it up: if you're a country boy or into oil & gas then Aberdeen is your place to go -
if you're more of a urban guy - I would chose Glasgow.

I think Floris has made it clear.

let me speak as a current student of Aberdeen (if you can decide afterward).

people - both lectures and students are from various nationalities. Specially lecturers, they are very approachable and expert on their respective fields. As Floris mentioned if u'd like to do Oil/Gas, Aberdeen is pretty much well-known internationally. Oil/gas Law housed a quite influential research center called Center for Energy Law. For your details plz visit www.abdn.ac.uk/law.

City - I have been to Glasgow but I simply did not like the city (maybe biased but different person has different taste). Glasgow is the biggest city in Scotland, very crowd as well, sorry to say but they city is dirty. Unlike Aberdeen, the city is clean and places more accessible easily because of the smallness of the city. Most people like prefer walking.

Facilities - apart from the Law library/Taylor library, the uni has its massive library which was officially opened in later summer last year. Taylor is bit old but it is convenient to study. Nevertheless, most students prefer studying at the new library. Here is the link: http://www.abdn.ac.uk/library. In addition to that, as said by Floris Aberdeen has its own sport facilities which is claimed as the same standard of Olympic; http://www.abdn.ac.uk/about/sports-village.php. If u fancy of going to the gym this is very cheap and it has all workout facilities available.

students accommodation (on/off) are varied. if u choose on-campus, you either stay in King's College (main campus) or Hillhead Residence which majority of students are based. Off campus, there is a range accommodation for students offered by privately-owned with affordable price too. Most of them close to the beach (if u are beach lover).

Overall, I like Aberdeen (uni, course, people, city) but I dislike the weather (typically in Scotland), you have no choice.

Thanks a lot for everything. i'll definitely choose Aberdeen.