The Garmin in general gives a longer battery life upto 8hrs I believe... depending on type of usage.
The TomTom gives a quoted 4hrs but I've manged 5+hrs on mine. The hands free bluetooth function works well but it really needs the external microphone for a clear conversation.
Both do 8 character postcode search.
The TomTom is very easy to navigate through and has a very good touch screen. Main gripe about it is it doesn't seem to take you on obvious routes although it does have an alternative route planner. Once at your destination and ready for home you need to check the route (rather than just clicking home) to see if it differs from the route it took there as it can take you an entirely different route! However it does have a favourites folder where you can save journeys.
I'm afraid I don't know to much about the Garmin although it does use different mapping (Navteq) although TomTom is now from what I hear using both mapping companies which include TeleAtlas.