Scizor, being a Bug/Steel-type, is better than Scyther, being a Bug/Flying-type.
Scizor is only weak to Fire(4x), while Scyther is weak to Fire(2x), Electric(2x), Ice(2x), Flying(2x)g, and Rock(4x).
Scizor resists 8 different types, whereas Scyther resists 3. They both have 1 immunity.
I'd go ahead and evolve it.