Having studied in RV and having many friends in PESIT I think I can fairly say there is no outright winner in this contest.

Both are private colleges autonomous under VTU.
Both colleges have great placements.
Both are automatic choices for the top rank holders in CET and COMEDK. But the general trend being RV ECE and CSE seats filling up first followed by PESIT ECE and CSE.
Both are seen as alternatives to NIT

Both have their shares of weirdness and red-tapes with college authorities. PESIT guys have their random walls. RV has a random museum.

When it comes to liberality I can safely say RV is way more lenient.

The number of clubs/activities that you can be a part of in RV is something in which RV has a huge lead over PESIT.
You can choose from RVQuizcorp, DEBSOC, CAT, CARV, RAAG, Rotaract, Vrithanth, Avventura, Kannada Sangha, Ashwa, Garuda, Chimera, Vyoma, RVCE E-Cell...and the list goes on

There is a great hackathon culture amongst the students in PESIT which RV guys are fast catching up on.

When it comes to fests, each department in RV conducts its own fest once in 2 years and 8th Mile>Aatmatrisha.

The RV campus is huuuge in Bangalore's standards. 64 acres with almost every department having a separate building of its own.

One thing that majorly distinguishes PESIT from RVCE is the marketing strategy of PES group of institutions.
PES group goes all out advertising the PES franchise. They even have a store inside the college selling PES merchandise. Whereas RV doesn't bother marketing their brand.

Also with PESSE now being renamed as PESIT-South it remains to be seen on how it will impact the brand of original PESIT.

The only difference between a RV student and PESIT student according to me is that it is impossible to find a PESIT student without an ID card. 

But at the end of the day students are the ones that make both these colleges great. The similarities far exceed the differences and ending up in either of these colleges provides one with loads of opportunities to excel in things they are interested in.