I use both Aweber, and get response. I don't have a personal prefrence over either of them. I just use them both to help build my lists with.
However, as I have read that Aweber can sometimes shut down accounts, and I do not want to lose my valuable time, and clients lists that I have built up already with my efforts, using both these service providers might help to avoid issues.
I do also tend to keep a file of all my subscribers just in case something should ever go wrong with either of these service providers. I do this as my own backup security measures.
Hope my answer helps with your question