I have used both RKSV and Zerodha. I vote for Zerodha
I think in terms of reporting, tax P&L statements, quant reports and all, Zerodha is much much better.
Pi and kite again are much better than NEST. What I have seen though is that if on PI i have opened charts with a lot of data on it while trading, then the entire user experience spoils. As far as there is not more than 5000 candles on the chart, it works quite well. But that said, I am using Kite now, because I think Kite is better than Pi.
The place where RKSV scores over Zerodha is in the call n trade bit. It takes a lot more time to reach Zerodha's dealing desk compared to RKSV. But here is the thing though, RKSV charges me Rs 25 for every order placed, whereas Zerodha charges Rs 20 for executed orders only.