I am a HUGE google fan - I have everything under the sun by them and I LOVE them. Having said that, however, I find their maps are not accurate occasionally.
Map Quest best 2 out of 3! Are they going to same route but just have different totals? If it's not that much of a difference, I would trust the Garmin.
Garmin all the way. The Garmin bonus is as you drive thru LA if it detects a long traffic delay it automatically reroutes you to the shortest distance. We LOVE our Garmin!