As a very new player in the Beta (though I knew SOME of the basics from the first game's campaign), Zerg scared me off due to the large amount of macro from either the creep tumors, queen's larva skill, and larva production. There's a lot to keep track of when first trying them out.
Terran I felt was too vanilla and was going to be one of the highest played since it is a Terran story in the campaign. Wanted something different, so I went with the last choice.
Protoss has a nice mix of both survivability and flexibility due to their shield regen, zealots charge, crowd control from Sentinels(?, LOVED throwing down those domes), and their macro was a very simple fire and forget build time reduction. Coming from other RTS's (mainly Command and Conquer), they made the most sense.