Japan Racing is pretty special. If I already had a standard Speedy with a black dial that would be my choice.
Just pick the one you like best. Long term, they're both going to be worth more than you pay now. Near term, Ultraman is a steal.
Japan racing. Certainly not a cheap option buying the 3570.40, but an easy mod if that way inclined and one I'm currently considering.
Ultraman for me: I don't like the dial color of the Japan nor the massive use of orange&red. The Ultraman chrono seconds hand is wonderful... S.V