Looking at getting a portable auto GPS for the wife (TomTom GO720, Garmin Nuvi 770, or Magellan 4250). Which is the best and is the traffic/wx feature any good. Does traffic/wx cost extra? Kind of like the hands free voice activation of the Magellan. What features are essential? Thanks. Just noticed the Magellan crossover for boat and car, anyone use one of these?