The Cathedral is by far my favorite. I wonder how long they took to master those stained glass lighting effects? I love how dark it is compared to the original, too, which had a lovely concept but never really resonated with me. It almost resembles a modern day Dead Space 2 setting, which is about the highest compliment I can give.
As for worst, the Bell Tower was my favorite arena from MK3 due to how dark and spooky it was, with that feeling of vertigo underlying in its presence. Now it seems too light-hearted in its appearance to find it spooky or leery. Also unimpressed with the Wasteland, but I haven't seen nearly enough of it to properly judge.