Gotta say that, while I do own and often use my dedicated Garmin outdoor device, I would switch to any other brand if it were for sale here. I am most disgusted with Garmins horrible support, lack of decent 'device to iMac and vice versa' support, the slow chips and the most loveable of all features: when you load any new map, we will overwrite all others.
Having switched from 1 windoze PC to an iMac AND a macbook, I find myself not being able to use as I please on both my computers my very expensive official maps. Bah. I am no fan of Garmin at all.
There is no better alternative yet though.
*rant over*
On the topic of GPS on iPad, I use Waze (which I also use on my phone) when driving, for reasonably up to date traffic info and a little fun and banter. When I actually need directions though, I will use the Garmin, for it's far superior maps. The Garmin will not come with me everyday though, so every now and then I do take directions from Waze and it works out rather well. My only gripe is that the map is not up to date, as is in fact the case with most nav systems I know. I live in a completely newly built area, and my street does simply not (yet) exist on most maps. It does show on Waze, but has no street name attached and I cannot navigate to it.
Oh well, one day.....
Waze suits me well for my everyday needs, and iPad offers me the nice large display, so that now I can read the messages when they appear!