Yes it is mandatory to surrender Indian pp.
It depends on your requirement, if you are sure you wont need to stay for more than 6 months eVisa or regular Visa should suffice, but these visa has restrictions placed on them. OCI gives parity on most privileges to that of a Indian Citizen except voting and procuring agricultural properties, not an extensive list.
eVisa will attract a separate lines in 28 Indian airports and few sea ports, while OCI will come under the regular immigration lines.