Basically, it would depend on how many subscribers you have. MailChimp is a good service provider.
If you do have 0-2000 subscribers and send email less frequently then you can just go with a free subscription.
But if you have more than 2000 subscribers and send emails frequently then you would really need a paid subscription.
Actually, I am currently using MailChimp. It is paid or free service depend on your choice. The free service is limited the amount of monthly email sending, but the paid amount will leave the limitation. for more information I think that you should go and check on the official website