I cannot decide which plan I need.

Ether Mailer offers only monthly subscription plans. All of them are based upon your total number of contacts (aka unique email addresses). The best way to determine which plan you need is to choose the one that covers the total number of your contacts.

For example, if you have 6839 contacts you will have to choose the plan with 10.000 contacts. The previous plan has 5000 contacts – too few for you.