Garmins are popular but over priced...
I would advise you to go to Fry's, Best buy or something and tinker around with them a lil bit to see which interface you're comfortable with....
Mio's a new player in the market and they make more affordable devices...
Tom tom and Magellan a relatively well known brands too....
But in my experience, we rarely got garmins back, tom toms and magellans were a different story,
can't comment on mio since they were a relatively new brand while i was working.
Personally, I don't like tom tom and magelan's interface.
The mio interface is fine, but garmin's are by far the easiest to use....
But for the price I'd go with Mio.
you can get a portable Mio for around 200$ way cheaper than the entry level Garmin products, and their portable ones start at $350 [i'm talking about the garmin 350 here so don't start with me about the 320 etc...]
But at just 150 extra the garmin 350 is not a bad choice, considering it used to cost upward of 500 or 600$ when in dec last year...
It all depends on your budget, if you want something cheap that works acceptably well, go for the Mio, if you don't mind shelling out a lil more Mulah, go for the Garmins