I would agree with the Smartphone based solution. Without pushing TomTom software on the phone specifically I would probably go for that due to the following;-
Best range of add-ins and POI farms available. Large user community and good update mechanism.
Smartphone also brings ability to use it for finding venues and food/drink etc when arrived with tripadvisor etc.
You can load a translator application to get you out of speeding tickets (I was told this by Boshley
)
You always need to carry your phone anyway so why carry something in addition.
You can keep all your favourite videos on it for the traffic jams and delays.
For occasional UK travel and emergency international use the real time map applications built into iOS and Android are great and have amazing overlays and content options from Google/Apple etc. They are also upgraded with each new version of the OS so continue to improve.
If you travel abroad I would certainly add TomTom or another application which carries its own maps as international roaming with data use is shockingly expensive. The built in map applications tend to download everything in real time and so can consume a lot of data. Two days out of country with roaming charges for sat nav can cover the purchase of the TomTom EU maps package if you are on the wrong tariff. Also if you are touring distant regional areas and you lose 3G signal the map downloads are so slow they are useless, very very bad in rough areas and late at night when you are trying to find the hotel !
A fried of mine bought a world sat nav app for $3 on Apple AppStore a few months ago to cover a US jaunt. It was not TomTom but it was completely acceptable for basic navigation. I think it was this one - http://itunes.apple.com/gb/app/gps-navigation-2-satnav-by/id329340711?mt=8&ign-mpt=uo%3D2
I would use a larger screen model like Samsung S3, Asus Nexus7 (needs to tether through a phone) tablet or iPad if you can fit it in so you don't end up in an accident trying to read it. The more common handsets give you more options over mountings and covers, you can get pretty much anything for an iPhone, for a Galaxy or HTC your choices are more restricted so consider these as part of the decision on handset. I would look into a bike comms system for the output from it. At a pinch the Bluetooth headsets (Motorola S9 is quite discrete and can allow you to answer calls as well as listen to music and turn information -
http://reviews.cnet.com/headsets/motorola-motorokr-behind-the/4505-13831_7-33418013.html )
The screen technology used in an iPad is called IPS and it has far better viewing angles than the cheaper technologies in other devices, This allows you to position the device in a broader range of locations around the cabin. It also has a higher brightness as Apple expected it to be used outside a lot. I would add the Galaxy S3 and HTC One range to this list of brighter screens. You will probably have to be careful of using reactive sunglasses as these can filter the picture on some screens so do check, or go for fixed tint pair.
HTH.
