Both are great detectors but they are designed for different uses. The Escort Redline is more geared for people that will mostly use the radar detector on the highway. Its also immune to all radar detector detectors so many commercial drivers opt for the Redline and also those users that plan to use radar detectors where they are banned such as Virgina & Washington DC and parts of Canada also love the Redline.
The Escort 9500ix while not immune to all radar detector detectors does however come with great benefits having an embedded GPS antenna. Using the GPS antenna the detector is smart enough to mark false alerts and memorize the frequency and the GPS location of the false alert so that it will never alert you to those false alerts in the future. It can also give you advanced notice of red light cameras and fixed speed cameras.
Both of these detectors are listed in the Best Radar Detectors of 2011-2012, If you live or travel frequently through areas where detectors are illegal and you plan to use a radar detector get the Escort Redline, If not the 9500ix will give you more for your money.