Thanks for the answer, NYPaddleCacher,
Coming from Europe, we prefer the East coast. I was never in the United States, but New York looks great; NYC, the capital Albany (smaller than Luxembourg city but looks charming) and the Catskill mountains. I think it is possible to visit this places and some more during 1 trip.
I found most of my caches in Luxembourg: we've about 4000 caches. A lot of lost places in the south, vineyards (east), highlands (north). The New York State looks also very varied. I also like the back land areas. :-)
15 countries; great! My last European country was Bosnia. It was a hard fight to find some caches there (caches ar rare there, connection failures... but finally we managed it) 3 tradi-Caches & 1 earthcache.