After analyzing all Joomla Extensions for newsletters I've decided that the Pro JNews component should be able to answer my demandings for a particular website that i'm working on. It was my first time dealing with this kind of functionalities so i was a bit over cautious and compared this component several times — even after the installation was done — with the other joomla components of the same kind (and others not joomla related). I realized this one is really the best for what i need. The documentation guide us very well, not only through the component it self, but also through the complexities of the newsletters world, with fundamental tips. The component's framework is very stable and intuitive, and basically it really does everything it claims to do.
I was also amazed at how thorough the support team worked with me when i needed, even in small details. I felt i placed an (very) important part of that website functionalities in very good and capable hands. I totally recommend it.