For Scyther, l think the best use for it would be Swords Dance or Night Slash.
l see no real use for Double Hit on Scyther, and with a +2 ATK from Swords Dance, it could be a great sweeper with 252 Speed EVs and a Jolly nature, that's quite a lot of speed.
Although if you really don't want Swords Dance, Night Slash would be quite alright. With a high critical rate, it could do a lot of damage if put to good use.
(+) Although, Cranidos does have a good point, l forgot about Technician. Even with Technician, since it's a Normal type move, it won't be as effective as Swords Dance powering up everything, or Night Slash for coverage with a high critical rate.
Double Hit would probably be for damage, but will provide no coverage at all. ~