Skorpion is the only effective dual-wield SMG. 3 bullets to kill within 12.5m means you will almost never lose an open shootout in your effective range, and the 5.85 to 7.8 standing hip-fire spread is tight enough to be extremely effective given the Skorpion's lack of recoil. The 160 bullet load-out is enough to get your killstreaks before you run out, so you won't need to resort to Scavenger, either, and can instead use Ghost, which is one of the best perks for CQB classes.
The only problem is getting caught reloading. Btw, SPAS-12 and Stakeout fulfill the same CQB role as dual Skorpions much more effectively and even akimbo, the AK74u and MP5K have equally low TTKs with Rapidfire equipped, so dual-wielding any SMG is never the best option... but they're definitely a lot of fun and don't require the same level of precision that a shotgun does.
The other dual-wieldable SMGs have higher rates of fire than the Skorpion, but actually have higher TTKs due to doing 30 damage as opposed to the Skorpion's 40 damage, which means they're a 4 hit kill and will run out of ammo insanely fast, which basically mandates Scavenger.
MAC11 is the second-best high rate of fire SMG to dual-wield due to having the best recoil profile. PM63 has a lightning fast two second reload and the Kiparis can shoot through people and walls like an AR, but they yank around a lot, waste precious ammo, and require more judgement than dual Skorpions do to be acceptable. --- Nolite te bastardes carborundorum. GamerTag: Vicelight, currently playing Call of Duty: Black Ops