recommendations for Registration-DB plugin?

Hello,

A potential client would like the ability to have a registration form on the site that collects user information (addresses, phones, emails, etc) that they could also add to manually from external lists and download from.

Is there such a plugin anyone can recommend? The purpose is not to limit access to the site but to collect data. Perhaps it should be done with an email program instead, such as the Mailchimp plugin?

Thanks in advance,
Antonella