Have an account with both,
1. Buy/sell on phone and online, Zerodha wins on both, call n trade I guess they have a much bigger team and ZT the online version way better than NOW.
2. Zerodha again, 40% of overnight margin requiremetns, cover order facility and SPAN calculator which tells you the margin before you make a trade..
3. Brokerage STO is better, but unless you make like a few 100 trades a month, shouldn't make a difference.
4. Both don't provide RT data, you have to pull it from the terminal.. So they are almost similar, but I know that you can get API's for NEST(ZT) which some of my friends use for doing fancy stuff.. API basically can connect any other tool to NEST..