What’s Your Favorite Email Marketing Application? Aweber, Constant Contact, or something else?

I’m needing an email marketing application and am most familiar with aWeber. However, it seems like Constant Contact is more popular and I would greatly appreciate hearing from anyone who has a strong opinion on these, or any other email marketing apps. What do you like best and why? Thanks!

We use constant contact for every e-mail campaign we promote and we love it!