I’ve been using ESPs for ~8 years. ConstantContact is a great way to go if you don’t mind their name at the bottom of your newsletter. It all depends on the flexibility you are looking for and the metrics you need out of it.
ConstantContact doesn’t have an easy “open rate view for a period of time” tool, which is nice to see what type of legs your email pieces have.
Also, finding ideal drop days and times is a little bit of manual work.
But, they are very reasonable cost-wise, and, very importantly, they are not seen by the major service providers or by most major organizations as spammers. The nightmare scenario is choosing an ESP and finding out that none of your recipients are receiving your message because the service you chose has a history of having spammers as clients.
