Ambipom is one of my favorite Pokes this gen, which is saying something seeing as I hated Aipom. In messing around with it, I've found it to probably be the best damn lead in the game. These are some Calcs with a Choice Band, and Ambipom can do way more:
Ambipom
#Technician#
@Choice Band 4 HP/252 Atk/252 Spd Jolly
Fake Out
U-Turn/Return/Double Attack
Brick Break
Shadow Claw/Payback
Fake Out is needed, it does a ton to everything. If you know Salamence isn't Choice'd, Return will 2HKO it, and OHKO quite a few things, but I like U-Turn 'cause that is pretty much the theme of my team, however I've been debating it with myself.
Brick Break is pretty much all you've got to hit steels, you can put Rock Smash if that's your thing. I still think people like it because it can be your HM whore and competitive Poke at the same time.
Note that Payback is 75 BP and 150 for switchins or getting attacked,(In other words, it OHKOs Dusknoir if it switches in on you and does like +40% to Metagross if it switches in) but Shadow Claw is a force against Fighting types if you don't like that.
Common Leads:
Weavile- Ambipom does like ~68% to it with Fake Out
Salamence**- Ambipom can either do ~33% to it with Fake Out or U-Turn out
Staraptor**- Ambipom does like ~39% or can U-Turn out
Gyarados**- Takes over ~28% even with max HP from Fake Out and can be U-Turned
Gengar- Most are Choice Scarf, so I would switch out
Heracross- Takes over 50% from Fake Out
Medicham- Takes over 60% from Fake Out
Shaymin- U-Turn does a lot, depending on EVs
Mesprit- U-Turn will do a lot, Shadow Claw CH nearly OHKOs 252 HP/Def Mesprit
Metagross- Will U-Turn out.
Slowbro- Will U-Turn out and finish it with Shadow Claw when weakened.
Milotic- Will U-Turn out.
Swampert- Will U-Turn out
Tyranitar- Brick Break OHKOs
Hippowdon- Will U-Turn out
Jolteon-Fake Out does over ~75%
Aerodactyl- Will switch out, but you do over 30%.
Crobat- Will switch out, but it does a ton with FO.
Sceptile- Fake Out does like ~68%
Ninjask- Fake Out LOL OHKOs
Zapdos- Fake Out does like ~40% on even defensive ones
Regice- After 2 Fake Outs Brick Break will KO Regice
Infernape- Hates Fake Outs, can U-Turn
Froslass- OHKOed by Shadow Claw, can U-Turn
Floatsel- Fake Out HURTS. Try over 70%.
Rampardos-OHKOed by Brick Break and will never outspeed Ambipom, even with Choice Scarf.
Bold is for things that take over 50% from Fake Out.
*All Calculations are done with Choice Band
**With Intimidate
Ambipom beats or gets quick damage on 23/26 of all common leads. Freakin' sweet.
So, yeah, Ambipom. Tauros, say hello to your cousin Ambi.