1v1's are really fun right now. Made my way through Gold league, got promoted to Platinum and rose to rank #1, but it won't promote me yet to Diamond.
I play Zerg
-Vs Zerg:I have been 10 Pooling against Zerg a lot lately. More often than not, Zerg's are 15 hatching against all races, they don't drone scout, and if you send an endless stream of Speedlings it just causes them to quit out. If they get Banes or survive, I saturate my natural and go up to Lair tech. A surprise attack of 6+ Mutas will usually force them out of the game.
-Vs Protoss:15 Hatch, with 2nd OL over my expansion to watch for cannons. Single Queen at main and double Queen at expo. Get Speedlings, scout for proxies, harass expansions. Drop 2 Spines at my expo, in case of a 4 gate all-in. Get 4 gas going asap, go to Lair while harassing, and drop a Spire and get 8-10 Muta's asap. If they counter with Phoenix, take a 3rd and transition to Speedling, Roach, and Hydra. At this point, I am scouting for Colossus and have Hive tech ready to get Viper's out if necessary.
-Vs Terran:15 Hatch, with 2nd OL over my expansion to watch for bunkers. Single Queen at main and expo, using creep tumors on both of their first 25 energy to get the spread going asap. Get a defensive Baneling Nest and Roach Warren. In the mean time, saturate the main and expo getting all 4 gas going asap. Build 2-3 Roaches to deal with Hellion harass, take a 3rd if they let me, play defensively while go up to Lair and Spire. Immediately have the bank, larva, and supply to get 10 Mutas as soon as the Spire completes. 10 Mutas will melt Missile Turrents and be able to take on a decent sized group of non-stimmed Marines if necessary, often leaving the Terran completely crippled and unable to defend their mineral lines. If they hold, transition out of Muta to Hive, make sure your 3rd is up and pump Ultra's.
Mutalisks are so good right now, that I incorporate them into pretty much all my strats, but you have to be prepared to transition out quickly because they can still be hard-countered. After playing with them, you will start to instinctively know that your Muta ball can destroy his Stalker's or one shot a Turrent and get out unscathed. They can pick off re-reinforcements or run-down retreating forces. They can find holes in the defense, cripple an economy and get out before the opponent has a chance to respond. They really are one of the best units in the game right now.