I like using my Garmin over my EVO for GPS navigation. I view it as a car appliance...and treat it that way. The EVO comes with me, and does my things...I let the Garmin take care of the directions.
I normally stream music in the car, and I keep my EVO on the Pandora app/widget so I can skip songs, of give a thumbs down easier.
If I didn't already have a Garmin, I probably wouldn't buy one though. I'd just use my EVO for GPS as well, but then I would have to buy a car mount. Also, with my EVO in the Seidio Rugged case, I'll need a generic mount, and I'll have to plug it in and unplug it regularly. Not my cup of tea...