if you have an iPhone or android device, save the money and use that one. I'm using my iPhone GPS which is more user friendly and better than the normal GPS'.

Let me know if you need any help with the istallation on your mobile device.

ALL of the models sold will allow you to select English in the setup.

I have a preference for Garmin models but both are very good. The best selection and normally pricing will be at Mediamarkt. If you can't get out there (behind the airport), you can go to a M electronics (Migros). They also sell them at Interdiscount (biggest store on rue du Marche).

You will want to get a model that gives you lifetime map updates. You then connect it to your compter/internet and it will update all of the maps.

You may very well be aware of it but as well as the media markt in Meyrin, there is one at route d'Acacias 43.

as each MediaMarkt is run separately from the other, as well as simlar goods, you may very well find some different stock in the both

sorry for typos

should read 

'as each MediaMarkt is run separately from the other, as well as same goods you may very well find different stock too, in them both'

As what Verbier says. I've bought both a garmin and tomtom in geneva, and both had English, French, German options along with other common languages. Both brands have good and bad points. You can also download free language packs online.

Nokia smartphones come with free navigation and Navteq map updates for life (of the phone). TomTom can be bought as apps for the iPhone/iPad and Android.