I'm using the Tom Tom Go 700. I really like it. It gives a few odd directions at times (ie. U-turns) but the directions and maps are really good and accurate.
I mount mine on the windshield and it is a little far away if you are trying to enter data while driving (but in the end really not a good idea anyways

)
I have not tried mounting it to the dash yet but I had read in a few reviews (while I was researching to buy it) that the suction is pretty powerfull and can damage your dash trying to get it off.
It was a toss up between the tomo tom and the garmin street pilot, and even though the garmin was a bit cheaper I decided to go with the Tom tom due to a better screen and features - and you can use bluetooth if that is your thing - not for me but good in the future I guess-
Hope that helps a bit? I can take pictures of how it looks set up and in use tomorrow if that would hekp you out.
Greg