I use Garmin GPSs in work trucks for rural responses in a 2200-square-mile county and I hate them...I've found that they're slow to respond, the menus and search functions are unintuitive, and they're slow to register touch. THAT SAID, they are relatively low on the offering totem pole. I have a different Garmin, bare bones, that I use for hiking. My experience with both is that when I get frustrated, I simply use my iPhone 5 with success. I've begun putting topo maps on it for hiking too, and use Theodolite and MotionX.
For these reasons, I have been actively NOT buying a GPS for the bikes...I guess I'm waiting for one to bite me on the ass in the Flea Market or fall into my lap or something. In the meantime I keep being happy with the iPhone 5, cached maps, and a good old paper backup in my tank bag. The only thing I'm having trouble overcoming it the visibility of the iPhone screen with the Lifeproof case in direct sunlight.
I know, whine whine.