It depends a lot on what you're wanting to do with the GPS. Personally, I wouldn't buy anything but Garmin. Not that the others are bad, but Garmin equipment and support is that good.
Here are a couple articles I wrote which might help.
Part 1
http://hunting.net/fieldjournal/fieldjournal_detail.aspx?nID=307
Part 2
http://hunting.net/fieldjournal/fieldjournal_detail.aspx?nID=316