Although ultimately, if the OP restores from a SuperDuper disk image, if their computer originally had Leopard on it, they'll end up with Leopard again.
Until we actually see whether or not completely restoring a Mac from a Time Machine backup drive will work well or not, it's difficult to say Time Machine is going to be as reliable as SuperDuper! (which ALWAYS works, as long as no errors are reported). However, if it is as reliable as Apple makes it out to be, then there's no reason to use SuperDuper!, Time Machine just gives you so much more...