Well, for one, I found the London system far easier to navigate than NYC. I
think that this is in part due to the fact that there is no "express/local"
service on the Underground, at least not that I am familair with or have
heard of.

There are some fast and semi-fast trains on the underground, though
only on the Metropolitan line north of Harrow-on-the-Hill, and not on
the Uxbridge services.