We have been using the Vitek 2 for several years now. I have not used any of the other systems, but we are quite happy with the Vitek 2. My only complaint is that the computer programming is somewhat tedious. It was obviously not set up by a lab person! Once you get used to it, though, it flows well. We are a small hospital, and are all generalists working in Micro. Because the computer isn't so user friendly, the techs who don't spend a lot of time in Micro have a little more trouble getting around the computer.
The ID and sensitivity testing seem pretty well set up and their knowledge base and expert system is very good. They also seem to be pretty quick to inform the users when there is a problem with something. They recently had trouble with PIP/TAZ on gram negative sensitivity cards, and are keeping us informed about when the reformulation will be ready (FDA has to approve it).
Their customer support people are pretty good. We usually get help quickly and issues resolved in a reasonable time frame.
Overall, we are happy with the Vitek 2 and I would recommend it.