My favorite crank length is what I rode for years and years: 171, the odd length that Sugino used for its Mighty Competition and Super Mighty cranks. I tried 175, and never felt really comfortable with it, but that may be from riding the 171 Mighty Compe for nearly 20 years.
Recently, though, I installed a Sugino AT on my bike (thanks to the spindle hunting skills of Jim Narlesky!), and it's a 170--so close to 171 that I can't feel the difference.
I suspect that if I had more bikes, I might have a greater variety of cranks, but it's a moot point right now.
nath dresser
spring green, wi