What car is better as in quality and MPG?
best MPG would be the Mini Cooper. Best combination of MPG and quality would be the Scion, since it is essentially Toyota.
BUT, since you have ruled out the Scion, then I would go with the PT Cruiser or the Mustang. The PT is made by Mitsubishi, and is on par in terms of reliability with the Mustang, but neither will get near as good MPG as the Mini or Scion, nor will either be as trouble free as the Scion.
Lastly, have you considered a Honda Fit? Or are you anti-Honda, too?