Hi Janine,
I use both Aweber and Constant Contact. Both have their pros and cons. What I like about Constant Contact is that the interface is a bit more user-friendly. I use it to design newsletters for a client of mine, there are templates to choose from, etc, etc. I am not sure if Aweber has any templates to choose from -- you can certainly create your own HTML template though and use it in broadcasts/follow-up sequences.
Aweber is great on the Autoresponder side of things. You can have multiple lists with multiple follow-up messages, broadcasts, etc. I also like being able to review reports for my clients. There are so many different ways you can review sign-ups, subscribers, verified and unverified leads. It is pretty neat if you like and need that sort of thing (which I think if you are going to be utilizing sign-up boxes and have many leads, using the reports and tracking is extremely important).
As far as price, you are right, I don't think Aweber has a free trial. Constant Contact does as long as you have 100 contacts or less (for the first month or something like that I believe).
So, those are just some of my thoughts on the two applications. If you have any questions about what I have said here, I will do my best to answer
