I bought a 'Road Angel 6000' for my wife at Christmas. (on offer in Halfords at �179 at the time)
She has had no problems with it and has just been form Edinburgh to- Aberdeen on Saturday, Newcastle on Sunday and Croydon today. Its taken her right to the door every time.
Unfortunatly it brings her back as well !
Has the added advantage of 'speed camera' and 'black spot' warnings programmed into its maps.
I haven't used any others to compare it with, but more than happy with the price/performance of this model. (sat nav not the wife)