Right now I'm in the practice league, and I decided to try something different and do a 2v2.
I did 3 games, 2v2 with randomly chosen teams, as terran.
First game
Terran & Terran (my team) v. Terran & Protoss
I head straight for them vespene gas collectors and make lotsa reapers. I use them to jump behind the enemy and kill all of their SCVs.
Match quickly ends in our favor but I forget the details.
Second game
Terran & Terran (my team) v. Terran & Protoss
See above. I get reapers and take the xel naga towers in the center for vision.
This game was a lot more interesting. I jumped behind the enemy and killed all of their probes, but after the second hit they were able to defend themselves.
I did manage to kill his first expansion shortly after with the reapers, though. Meanwhile, my ally started making vikings and battlecruisers.
The enemy made colossi and stalkers, his ally made tanks and rines. We controlled the center.
Enemy terran sent his army into the center, where I had tanks and a horde of marauders waiting.
The protoss then began picking off my tanks with his army of colossi, retreating whenever my ally sent in vikings( though we killed a lot of colossi)
Using scans and sensors, we'd pick off all attempts to make expansions and basically had them locked in their base.
After a few unsuccessful attempts at nuking us and running out of resources, they surrendered.
Third Game
Terran & Terran ( my team) v Terran & Zerg
Reaper spam again. I got a lot better at the spam part of this and had a sizable army. I jumped in and killed the SCVs and zerg drones as my ally assaulted the front with marauders and rines.
We didn't break through the first time and the terran began making tanks. My ally was able to push through into the zerg's base, and while the terran's forces were occupied I used reapers to kill his factory and then some of his scvs.
Scans showed a zerg expansion that was sneakily made while we were busy, so I jumped in with the reapers and killed it while my ally did another push into the zerg's main base. Another jump in and the terran died, followed shortly by the zerg.
I love 2v2 now, I can focus on the skirmish/ harassment part of the game, which I like, while my ally makes more solid-attacking forces. Eventually, if the round goes on long enough I push up into marauder/tank spam. I love my reapers, though. Scans and reapers can give some pretty low risk victories. I find striking add-ons to be particularly effective early as well, especially when they have no extra factories/barracks and low vespene income ( as a result of me killing their SCVs).
On the subject of the zerg, I find them to be weak compared to the other races. The only unit I like for zerg is probably the brood lord. I want to like the roach, I really do, but it just seems too weak. Hydras also seem weak.
The protoss are strong contenders but I haven't played enough with them to get a feel for them yet. They seem to have a lot of tricks up their sleeves this time around.