Game #1. Like a few others have said (JavalTigar), it's a training issue. Basically, I want to get comfortable with the game, learn what new things have been added or what old things have been modified. For instance, ICS is gone, so you'll have to get used to a completely different tempo of build-expand-attack. And with the change to units (no A/D, promotions), combat will have an entirely different feel to it.
Basically, when you're learning something new like that, adding more variables to the mix (like a random map) just confuses the issue. So, I'll play world map first, because it's the least confusing way to begin. Now, in the long term, I probably won't play it much at all.