I personally prefer the Garmin. I have nuvi 255 and 205 reasons for having 2 
My family bought a TomTom for my dad and its all right for general navigation.
TomTom are ok but even with their IQ route they use different and less accurate satalites than Garmin and they have something similar to IQ route in low models anyway.
The Garmin are the ones also that the military use.
On foot they are hard to beat and a small package so easy to carry around so it does not get stolen from your car and last several hours on a single charge for foot use.
But generally any of the major brands are ok. but once you get the features and extras you want thats what will make up your mind.

My family bought a TomTom for my dad and its all right for general navigation.
TomTom are ok but even with their IQ route they use different and less accurate satalites than Garmin and they have something similar to IQ route in low models anyway.
The Garmin are the ones also that the military use.
On foot they are hard to beat and a small package so easy to carry around so it does not get stolen from your car and last several hours on a single charge for foot use.
But generally any of the major brands are ok. but once you get the features and extras you want thats what will make up your mind.