Standardzor
Scizor@Choice Band/Life Orb/Muscle Band
Adamant nature
Technician
252 Atk/252 Spd/4 HP
~Bullet Punch
~Bug Bite
~Aerial Ace/Wing Attack/Swords Dance
~Superpower/Rock Smash
Pretty much the standard issue Scizor set. Bullet Punch is your main attack. Steel may have horrendous coverage, but what essentially amounts to base 90 power priority (10 higher than ExtremeSpeed and Sucker Punch!) is nothing to sneeze at, not with that Attack stat. Bug Bite is Scizor's other preferred STAB move. Due to being at 60 base power, between Technician and STAB, that's 135 base power right there. X-Scissor's not sounding so hot now, is it? And that's not even going into the possibility of swiping an opponent's berry! The third slot depends on your item. Aerial Ace and Wing Attack are for all intents and purposes the same thing, given the popularity of evasion clause, so unless the lower PP of Aerial Ace doesn't appeal to you for some reason, either one works. Swords Dance, it goes without saying, is only if you're not running Choice Band. As for the last move, Superpower is preferable if you're running a Choice Band set. The stat drops won't matter, as CBers tend to switch a lot anyway. Rock Smash is significantly weaker, but does get a Technician boost, AND has that sexy 50% chance to lower the foe's Defense.
Choice Band is the item that you'll probably see recommended the most, and not without good reason. Essentially +1 Attack is nothing to sneeze at, even if it comes at the cost of being able to switch attacks. Life Orb doesn't provide as much of a boost, but it does allow Scizor to freely change which move it uses. Muscle Band provides an even smaller boost, but unlike Life Orb, doesn't hurt Scizor, allowing you to potentially fake a Choice Band. Scizor hits so hard in any case your opponent is unlikely to know the difference.
As for the ability, only go with anything other than Technician if you lost a bet. Light Metal isn't worth it, as Scizor's Defense is too high for it to worry about Low Kick, and it resists Grass Knot almost insultingly easily. Even if Low Kick IS an issue, not worth losing the extra power from Technician. And Swarm... no. Just no.
Agilizor
Scizor@Leftovers/Focus Sash/Muscle Band
Adamant nature
Technician
252 Atk/252 Spd/4 HP
~Agility
~Metal Claw/Bullet Punch
~Bug Bite
~Rock Smash
Scizor has fantastic Attack, we've already established that. But what about its Speed? Base 65. Rather disappointing, when you consider what its pre-evolution, Scyther, is capable of. But, there's one thing here- Scizor gets Agility! With one move, Scizor achieves 458 Speed to complement its 394 Attack. Looking scary already. Metal Claw is actually the preferred STAB move here, achieving 112.5 base power between STAB and Technician. Agility makes Bullet Punch somewhat moot here, unless you really fear priority users. Scizor isn't frail by any means, and there's no priority Fire moves, so go with Metal Claw. To add to Metal Claw's appeal, it has the chance to increase Scizor's already sexy Attack stat by 1 stage. Swords Dance it ain't, but it's still a scary thought. Bug Bite is obvious, and NO SUPERPOWER HERE. You do NOT want to use a move that LOWERS Scizor's Attack! Not with this set! There is NO switching involved with this. Rock Smash is the way to go (can't believe I'm saying that).
Leftovers is the item of choice here, allowing Scizor to heal off any damage it takes while rocking the Agility. If, however, you live in fear of Fire, then by all means run a Focus Sash. Muscle Band is also acceptable for that little bit of extra Attack power.
Technician. Technician. Technician.
Specszor
Scizor@Choice Specs/Life Orb/Wise Glasses
Modest nature
Technician
252 Sp. Atk/252 Spd/4 HP
~Vacuum Wave
~Silver Wind
~Ominous Wind
~Flash Cannon
Yes, I see its Special Attack stat. I do notice, however, a few things. One, it's at least higher than that travesty of a Special Attack stat what that burdens poor Heracross. Two, Scizor has an actually decent Special movepool, made even more decent by Technician. And three, it has access to not one, but TWO moves that have the chance to increase all of Scizor's main stats by 1 stage each. Including Special Attack and Speed. Namely, the STAB Silver Wind. And Ominous Wind, which also gets perfect coverage alongside Vacuum Wave, Scizor's only special priority move. Hell, the only special priority move, period. Flash Cannon for STAB.
Choice Specs gives Scizor's poor Special Attack a much-needed boost, but doesn't give it the freedom to swap between moves. And with Vacuum Wave and Ominous Wind, moves that have stuff that's immune to them, this can pose a problem. Life Orb gives Scizor more flexibility, but less of a boost, and the recoil might catch up to you. Wise Glasses gives the lowest boost of all, but no recoil.
Technician. Technician. Technician.
Partners:
Politoed for starters. The rain waters down (really bad pun intended) the Fire moves that would otherwise spell Scizor's doom. It's also nice to have a Flash Fire Pokémon at the ready. Switch it into the inevitable barbeque and profit. Another nice partner would be... well... basically, any Magnezone counter.
Counters:
Fire. Just fire in general. Anything with a Fire move will render Scizor useless unless Scizor can kill it first. Aside from the obvious, Scizor users should be wary of Arbok, and I know this from experience. Arbok can carry Fire Fang, and Intimidate waters down Bullet Punch enough to let Arbok strike back. Even scarier these days, given that Fire Fang now benefits from the Attack AND Accuracy boosts of Arbok's new toy, Coil. And the Defense boost from Coil also waters down Bullet Punch. I myself have been behind many Scizor KOs at the hands (figuratively speaking) of an Arbok.
Oh, yeah, and Magnezone is generally bad news for Scizor, especially if it's already gotten the stat drops from Superpower, or is locked into another move.
I like having credit for my work. About the 4x weakness for Fire: I just wanted to make a point that fire ruins you. Maybe I've gone a bit to far...