Judith said
7 months, 1 week ago: Hey, Jenny….
Here’s a quick breakdown for you! 
=> MailChimp is pretty full featured newsletter and list management tool that I use it myself. I also recommend it to my clients not only because of all the needed features — but is has a user-frienldy interface and system that holds your hand as you learn about all the features and tools available for your use.
=> AWeber has more of a learning curve, is more robust with better tracking tools but an excellent choice for the more experienced marketer. For most of my client’s MailChimp’s tracking info suffices.
=> OptimizePress is one of several WordPress themes that create landing and squeeze pages that will have the call to actions for folks to sign-up for your newsletter. So OP works in concert with your newsletter service of choice. For these applications I prefer Premise by StudioPress and can vouch for their support too!
The key to using any of the above is going through the tutorials and taking the time to learn so that you understand all the features available and can use them to your advantage.
Does that help? 