I am currently studying in SRM Rapuram,so I can answer this question with my perspective.
Talking about the campus,when I joined the college (2015) there was no such campus thing here,not evern roads.Its true that the ramapuram campus is way too small then KTR.There is no campus life inside the college. But that’s a plus point too cz it’s in the center of city.for Ramapuram students the campus is whole chennai.Airport,beaches,malls everything is nearby.Other then that there is no crowd and rush in this campus so you can do pretty much what you want to(no college politics).
Talking about placement and studies, its same.placement is exactly the same for any campus.Lot many university rank holders are from Ramapuram campus.
Other then that, activities and exposure is less in Ramapuram campus i.e tech fest like AARUSH and cultural fests Like Milan used to be held in KTR campus but anyone from any campus can participate there.
So if you are looking for a wonderful campus life experience no doubt KTR is best.But if you think your college life depends on your friend circle and not in the campus infrastructure, enjoy the life being in Ramapuram.