You don’t have to bother about selecting one between CDSL and NSDL.
To invest in shares, you must have a Demat account and you can have a Demat account provided by either NSDL or CDSL, the only two Depositories in India who extends various services to investors and other participants in the capital market like, clearing members, stock exchanges, banks and issuers of securities. They also offer basic facilities like account maintenance, dematerialisation, rematerialisation, settlement of trades through market transfers, off market transfers & inter-depository transfers (CDSL to NSDL and vice-versa), distribution of non-cash corporate actions and nomination/ transmission. They extend demat services through agents who are called Depository Participants (DP).