Which one is right for me?
This depends on your specific but unknown use case. You need to add a new root certificate only if you need to verify certificates which were directly or indirectly issued by a yet untrusted root certificate.
Note that adding a root certificate does not help in the common case of a misconfigured server which fails to send the intermediate certificate.
Why are there so many?
Some of these root CA come from acquisitions of other CA like CyberTrust. Some are used for different purposes - like issuing normal certificates vs. issuing EV certificates. Some have different types of keys, i.e. RSA vs. ECDSA.