I would have to say the Muncie, due to availiability alone. The Saginaw is not strong enough when compared to the Muncie or the Super T10. Parts for Muncies are all over the place, kinda like small block Chevy's'. An M22 is going to cost you a bunch for very little difference in strength. Look for an M20 or M21 depending on what gear ratio you are looking for. You can purchase a new M20, M21, or M22 with the new Super case from 4 speeds.com.
Vince