If you read the reviews about them you will find that the "best" on the market at present are Tom Tom closely followed by Garmin. All you need to do is work out how much you wish to spend and which features you need.
Can't go wrong with a nuvi. Garmin makes a great GPS. I have a Tomtom. I used to use but I find my phone to be a much better gps than the Tomtom series. From my experience in sales and with most gps devices the Nuvi is a good device. I find the gift card to be a little impersonal esp for your father.