At the moment, I'm using GetResponse, Mailchimp and Wysija. I dropped aweber almost two years ago when they weren't able to prevent hackers from accessing people's mailing lists. I haven't heard anybody complaining in the past 6 months or so -- so I may go back to them. I actually prefer aweber over the others.
I heared aweber is the best but they are just too expensive for me so I use mailchimp. But I'm very satisfied with mailchimp, they have a very good inbox rate and I find them to be affordable so I don't think I will leave them any time soon