I just switched to random last night. Played about 10 vs the AI matches with zerg. I need to tweak my build order but I won several games as zerg. I started with Protoss and switched to Terran a few weeks back to learn them. So, now I have fully switched to Random.
I don't know who I prefer. I know playing Terran is the easiest team to win with. However, I love dropping Zerg worms and then storming bases with hydralisks and ultralisks while my mutalisks flank the base and take out all the workers.