I had the same decision last year as re-located to Australia. I bought the Navman over a separate unit for a couple of reasons:-
- The "outdoorsy" type units didn't seem to do good navigation and the car ones did poor navigation
- Can get the maps for UK/Europe/US/Australia, and its PocketPC so if wanted to go off map could just get a different software provider
- PocketPC gives me flex to add nautical charts for sailing (as a back-up to my laptop on the boat), and add topo charts etc for hiking
- Has an integrated GPS antenna so less cumbersome than one that clips on.

Has worked really well for me, and would still go this way even though I use none of the PocketPC functionality (use Blackberry day to day) - so not sure how it would compare to others (though know it has no Bluetooth or WiFi which might be a handicap for some).