The Gadget Show on UK TV test GPS systems every year, and in the past 3 years the Tom Tom has come top, with the Garmin a very close second, the rest have been a must try harder.
Treat them as a keyboard and try them out in the shop first, as each OS has its own quirks.

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).