Any email product or service you will use consistently. By use, I mean you will create meaningful messages targeted at your specific profile. By use, I mean a resource you will schedule to put out regularly and include information your prospects can use (don't just email when it strikes you).
Most of the email products are the same when considering what the email recipient sees. Where they differ is how intuitive are they to the new user - so the requirements to build solid, effective email campaigns are not an obstacle that is pushed aside because you can't figure out how to use them.
Here is one last tip - don't position your email program as a sale each time you send one out. Position emails as useful information to your prospect - something they get used to seeing value in. Two things will happen. They will open your emails regularly. Second, they will buy from you sooner, rather than later.