The main campus is good in that it’s beautiful and large. It also has a suburban railway station (Potheri) right opposite the main gate so traveling to the city should be easy.
As for the people there, you will feel right at home since many north Indians study at the main campus. The food courts are awesome and most of my friends are either living on campus or at apartments nearby. You must do some basic math on what works for you financially.
I have spent enough time in both Chennai and Delhi for me to tell you Chennai will never get as hot as Delhi. The dry heat of Delhi sucks. We have the sea there to cool shit down. The main campus, being rich in trees, will not let the temperature raise beyond a limit.
Take SRM and take the main campus only if you get a good course. And lastly, remember that everything (literally everything) in SRM has a price tag.