I know Scyther has less attack than scizor and less defence, but it has more speed and can learn more flying moves.
Which one is better for fighting with?
Definitely Scizor. Scizor is pretty much the most powerful Pokemon EVER (besides Ubers), and is a huge threat. Try this moveset:
Scizor @ Leftovers
EVs: 208 HP / 48 Atk / 252 Def
- Bug Bite
- Swords Dance
- Bullet Punch