Philly is ground zero for both bike theft and uninsured psycho motorists, so I would go for something that's both brake friendly and inconspicuous (not a keirin frame).
If you're looking for a frame that will last a while, most any Taiwanese frame will do. Let's not kid ourselves - a (new) frame is probably the part on a bike that's least likely to fail except in an accident, and nothing's going to help you there but your stopping distance.
If it were My One Frame? i'd get the bareknuckle. it's a little bit more versatile with brake mounts and a threadless steer tube. if i were in the market for a Pretty Bike i'd get a keirin bike, but i like something utilitarian - a little bit more in the All Arounder direction on the spectrum of bikes.
Depending on your size (as the keirinculture thread reveals),
the Keirin frame might be a better value. Myself a few other
shorter riders here have all done very well with used Keirin
frames. I was shopping for a Barekunckle before I stumbled
upon an old Bridgestone in my size for $450, with a bottom
bracket, headset and Nitto B123 track bars. A comparable
setup with the Bareknuckle would have run me $600-$700.
If you're really worried about theft, just take the stickers off
and you won't have too flashy of a bike, as long as it's not a
sparkley, tri-tone 3Rensho or anything. If it does get stolen,
then you'll have less invested in it than the Bareknuckle.