Being an alumnus of SRM University, I can definitely say that Kattankulathur is the best campus. The campus has two blocks and a lake adjoining it. The main campus conducts classes for mechanical/electrical etc and has majority of workshops there. The other campus has hostel as well as colleges for other major branches of engineering like civil, cse, ece, mca, mba, biotech(a separate dedicated building), designing etc. The main attraction of this block is the 16th floor library and Tech park. The campus also offers many hangout places and has various cafes and restaurants. Other than that it has several play grounds and ATMs and auditorium(which can host as many as 3500+ students). Also Kattankulathur campus is about 50km away from the main city and is about a stone throw away from the potheri station from where you can readily get local to travel to the city. Majority of events and fests are held in the main campus only and students from the other campuses (Ramapuram and Vadapalani) visit the same. The placements drives are held in KTR campus only and no matter which ever campus you are studying in you will have to attend the drives in this campus only (the reasons being the world class infrastructure and the T.P. Ganesan auditorium which which has an awesome capacity as I mentioned before).
All I can say is that SRM gives you one of the best campuses to enjoy your undergraduate life. The Kattankulathur campus is a world in itself and you get to see so much of diversification and people from varied cultures. I hope this gives you a fair idea about the main(Kattankulathur ) campus