The most challenging maps for you.

Are you saying that there aren't any maps more challenging than "Lake of Plague"? Then try playing maps like "Podarok 2001" or "Prodigial." I consider them to be my benchmark. It's true that something was left unfinished in "Prodigial" (you can ignore the last battle), but overall, I spent about 14 months on it! And the other one is even better, it's several times more difficult – about 20 months.