The company I work for has had great success with the Mitsubishi system including tech support out of Atlanta. We have had there tech support people just show up at our office wanting to spend a day looking at out jobs. The over the phone tech support is fast usually within a half hour or less.
If you decide to go with Mitsubishi go with a Diamond dealer and designer it will give you a additional 5 year warranty.
We have bid a job to replace a Diakin that has only been in 4 years at a college due to control issues and difficulty getting parts in our area.