Haro MTB for commuting and a LHT for everything else.
Originally Posted by degnaw
Bike size doesn't matter when choosing lock size. The size of what you're locking to does.
Agreed. Your son is going to need two locks anyway (one to lock front wheel to frame and the other for the rear wheel), so get him a medium and a mini and/or cable and he'll be set for most places he'll lock up
Some bikes. Hell, they're all the same, ain't they?
I use a Kryptonite Evolution Mini (wheel-to-frame) and a chain like the New York Chain (other wheel-and-frame-to-post). No cables unless you want to donate a wheel to a thief.
Get a U-lock big enough to lock whatever you need, but don't get one that's so big that a thief can stick a car jack inside and pry it apart (if you "fill" the U with the bike frame and the object you're locking to and don't leave room for a jack, you should be OK even with a bigger lock). When using the chain, make sure it's high enough that a thief can't hold it against the pavement and use another object to hit it and break it.
Sure, this isn't NYC, but it's DC. Go big or go home.