I would not focus on 20 or 24 gears. Most likely both bikes will have more than enough gears.
More relevant is steel vs aluminum & 406mm vs 451mm wheels. Steel is much more comfortable to ride, and 451mm tires are difficult to source, making 406mm better ( since you will have options ).
I like the NWT, honestly I don't understand how Allen advertises 451mm wheels as superior....they are actually inferior for most applications.
Thanks,
Yan