Euros are widely accepted throughout Switzerland but in every single transaction you are subject to the rate of preference adopted by those you are dealing with - this may be more or less what you would get at a bank but it could go against you. Rounding up will not generally be in your favour. As to where to stay, this all depends on which route you intend to take to Italy. You could stay in the Geneva/Lausanne area for the Aosta route, or else Luzern/Zurich/Lichtenstein area if aiming for the Italian Alpine lakes.