Aweber is a pretty good service.

Of course, other better "online" autoresponder services include:

GetResponse.com
ConstantContact.com
1shoppingcart.com

"Own Server Hosted" autoresponder systems include:

AutoresponsePlus.com or arp3.com (they are moving home at the moment)
ListmailPro.com

The effectiveness and deliverability rates of Own server hosted autoresponders often depend on the hosting account on which the script is installed in.

However, all autoresponders have a bit of a learning curve to overcome at first.

Separately, you'd want your autoresponder to have a high rate of successful deliveries.

Oh, and the answer to your question is: it depends... on your past experience with autoresponders, on whether you'd be working with lots of bulk and/or co-registration leads, do you have an existing database to migrate to the new service...but Aweber is a good service : )