I've talked to a few stockists of bushwalking GPS with the following results -
The Magellan dealer said that Magellan were better but the reasons why were far beyond my comprehension - something to do with an extra layer of mapping or something
The Garmin dealer said that Garmin was better because Garmin had better customer service
The dealers that stocked both either had no preference or admitted that they didn't really know much about the products.
Does anyone have any information or thoughts as to which is better for bushwalking?