I've had garmin and tom tom and while they both do a good job, the most intuitive was Garmin. It easy to use and you don't have to have a degree in sat navs to turn up the volumne. I also like the shape of the smaller garmin ones as you can put them in your pocket for walking and cycling... as if I do either!
I lent it to someone travelling from London to Liverpool once. After an hour he called me because it kept taking him to parks.... it was set for cycling.... duh!