I'd say that Germany, Austria and France have the greatest castles.
I've been to england an the castle...was more like a palace...
I've visited just one French castle and...uhh In Germany and Austria I visited:
Burg Waldeck, Burg Lichtenstein, Hohenzollern Burg, Burg Teck, Zitadelle Spandau, Burg Hohenneufen, Burg Landsberg, Burg Hochosterwitz, Schloss Tübingen, Schloss Heidelberg! The german word Burg means castle, Schloss means sth like palace, Zitadelle means citadel.
And my favourit is the Austrian castle Hochosterwitz! It has got 12 or 14 gates (ohh no, I forgot
), it is on a hill and it's huge! The interior contains very many weapons and armours. The castle got never occupied!
And I've seen very many other castles and palaces and ruins from far.