Deano747;269942 wrote: Have used both and find them both good for sealed roads in the North. Cannot comment for off road stuff.
The Garmin maps are "made" with the information supplied by ESRI with some of the detail removed so they can fit more countries on the SD card. For general riding around, I don't think that you will find any difference.
One area that I used the extra detail of the ESRI maps was in my pre planning. When I was picking lunch stops for the group I brought up last November, I would pick the town or village that I thought I would be in around lunch time and then zoom in to a 50m scale on my Zumo and troll slowly through the town or village. At that scale, most of the bigger eateries are displayed, and in quite a few of the towns, there would appear "recommended by xxxxxx" beside the name of the eatery. That made my choice of stop easy. The Garmin maps don't have that sort of detail on them.
I had the ESRI map on my Zumo for the trip around as I had done all my planning on it, and one other member of my group had my Garmin SD card in her Navman and she reported that everywhere we went, the GPS map was spot on. As I said, it is really the same map, just the level of detail that is different.
One thing that may be important to you, the ESRI SD card is locked to your GPS unit. You have to give the serial # of your unit to them when you order it, so cannot be used on any other GPS, whereas the Garmin SD card can be used on any compatible GPS.