On the resolution I use (1600x1200), many maps (especially older ones) have a bad visibility/readability, since they are made in much lower resolution. Because of that, when I joined CC, I played Classic exclusively (since I new it by heart and wasn't dependable of what I could see). After ten or so games, I was ready for other maps.
My first (actually ETERNAL

) love has been
Age of Merchants map. Even today, it's perhaps the very best map on CC, if you really count ALL (visibility/readability, logic of play, balance, beauty...)
About simple maps... It depends what degree of simplicity you demand. BY FAR the best plain map is
Battle of Actium. If it isn't simple enough, I vote for
Bamboo Jack. If you want simpler yet, I have two votes
a) for the best (though I don't like it very much) -
World 2.1b) for the loveliest -
Tamriel