For several years, I have been a MailChimp trainer. During the training sessions, I am often asked about CRM solutions that work with MailChimp. There are several options and one that I like is Capsule CRM.
Capsule is a cloud based system. You can login to it via a website browser or via their App (which is very useful). You can create a free account and experiment with it (with up to 250 contacts).
The best CRM (Customer Relationship Management system) for your business is the one that you actually use.
I have read countless stories in the marketing and business press regarding complex databases, that have cost a great deal of money, which have failed.
Many CRMs are too complicated and take too long to learn.
You can install a CRM on your own office server and there may well be good reasons for doing this, i.e. if it integrates with your accounting / e-commerce system.
Alternatively, you can use a cloud based system. This option can be easy to implement and inexpensive to run.
MailChimp and Capsule and be linked together via an API (Application Programming Interface).
I have got to know the Capsule CRM well as we use it every day within The Marketing Compass and I offer Capsule CRM training.