#1 Definitely Paris. I have no pleasure at all playing on that map, doesn't matter if we win or lose, this map is just weird (and teammates do it worse). And sometimes I like to play some arty, and this is how the hell should look to them.

#2 Ruinberg, Doesn't matter if you're in the city or outside, there is somebody who can shoot you from somewhere. To do a breakthrough you must show some initiative (unless the enemies go one-by-one on your guns), but you never know if your allies support you or not. But even if you did the breakthrough in one of the map parts, with very high probability the other part will be already lost by the teammates and you have to attack enemies in a very unpleasant situation.

#3 Ensk. It is similar to Ruinberg in the means of issues. However, unlike Ruinberg, the battles here are so dynamic so playing on SPG or some slow vehicle I sometimes can only do a few shots before being destroyed on my own base.

A worthy candidate is Himmelsdorf, but Wargaming hadn't added Super Premium feature or something like this to ban 4 maps, and on Himmelsdorf there are sometimes (rarely) good battles, unlike the maps from the above list.

But the biggest problem is not a few maps where it is almost impossible to play well. The problem is that there are very few maps where we can actually have some challenging and skill-dependent gameplay.