Definitely Switzerland! Germany is not cheap by any means, but
compared to the Swiss, all other European countries are more reasonable.
Food is probably the most expensive and a simple burger might cost
you between 15 and 20 USD.
On the other hand, Switzerland is a very beautiful and picturesque
country and definitely worth visiting.
One option would be to stay at the Bodensee on the German side,
and make day trips to Switzerland or Austria, as all 3 countries come
border there.
http://www.bodensee-travel.de/angebote/gfx/karte.gif
And here a pictures of some of the towns around Bodensee
http://outdoor-pictures.de/bildarchiv/bodensee/kn.html