I've had Garmin and Humminbird combo units, IMO I'd rather have a bigger black and white screen than the smaller color screen.
I liked the GPS on both Garmin and Humminbird.
One nice feature I've seen on some GPS's is where the red and green channel marker poles and bouys are loaded in the GPS map. That is a feature I want on my next unit.
I never really use the water temperature readings, so that feature is kind of just a bell and whistle IMO.
I like having different alarms on the unit, such as: low battery alarm, shallow water alarm, almost out of fried chicken alarm etc. etc.
I really thought the sonar was easier to read on the Humminbird and had more layout/display/sonar settings.
The GPS on the Garmin is pretty Awesome especially with the Bluechart? chip
Every Lowrance unit I've played with on friends boat's seemed hard to use...