I'm a big fan of Constant Contact. ACEware uses it to send out its monthly newsletter (the one you are reading right now) to customers who have opted to receive it.
Student Manager also has a great email tool as well that allows you to send emails to any contacts within your Student Manager database. Basically, any query /report you can come up with, you can send an email blast to that address as well.
So is one tool better than the other? For me, the answer is both tools have important niches in your communications with customers and potential customers.
Constant Contact allows you to have very complex and graphical emails that can be created with little trouble. The ability for customers and potential customers to subscribe and unsubscribe without staff help is really helpful, especially for a newsletter. That's Constant Contacts big strength... creating and managing your newsletters.
Student Manager's email blast power lies in being able to send quick emails to specific groups of names in your database. (Very targeted marketing).
Examples: Just created a level II class...send a email blast to everyone in the level I class about the new class. Instructor sick...send everyone in a specific class an email with makeup class information. New Photoshop class... send everyone who has the interest code "photo" a quick email about registering for the new class.
If you haven't worked with the email blast feature in Student Manager, contact your tech and they can walk you through how to set it up and use it.