The New York subway is a remarkable piece of engineering. It was built about 100 years ago and seems to have benefitted from lessons learned during the construction of systems in other parts of the world. Most notably London.
Price. New York wins hands down with a paltry $2 to ride anywhere in the system. And it's a big system. London prices for Zone 1 are heading up to £4 in the New Year. Ouch. Although London does have the advantage of the Oyster Card which can be conveniently tied to your credit card for auto-top-ups, and caps the fare at one-day travelcard prices if you travel enough that day. New York definitely needs one of those.
Speed. Contrary to popular belief, London trains do occasionally hare around the network. Early in the morning and towards the extremes of the system, trains can get up to an impressive 60 m.p.h (allegedly). New York trains don't travel quite so fast between stations, but they do have the remarkably neat Express Line concept - tracks that run parallel to the Local lines, but skipping all the useless stations that you don't want to visit. This makes it a breeze to travel the length of the New York Island, you just have to remember to get off at the right place, or you'll end up a long way from your desintation.
Buskers. London Underground just recently made busking legal, and even then only in designated places, and according to a strict rosta and licencing requirement. The New York Subway swarms with buskers - and they seem particularly fond of 14th St Union Square station. We've seen midget Michael Jackson impersonators, tap dancers, 14 piece swing bands in black tie at 7am and the ever present Ubiquitous Peruvian Band. It all makes for an enternaining (if noisy) experience when you're trying to get from A to B.
Claustrophobia. New York Subway trains are pretty wide, they're very long, and don't run very far underground. London Underground trains are the complete opposite. New York does benefit from being sited on some pretty tough bedrock which means the tunnels don't have to be quite so deep, and it makes a tangible difference.
Cleanliness. Travelling in London recently reminded me how much I appreciated a system that didn't smell of wee, didn't have so much litter flapping around, and wasn't so generally run down.
The New York system runs 24 hours a day. That's pretty convenient.
London station turnstyles are cleverly set up to allow traffic in or out of that particular gate in one direction only. This seems to lead to a lot fewer fights and delays.
Rush hour in both locations is a deeply unpleasant experience.