What region should I choose for Starcraft 2?

Solution 1:

There doesn't seem to be any significant difference between number of players/skill levels at the lower tiers.

Maps cannot be uploaded to the EU server by, let's say, an NA mapmaker without an EU account, but they can be shared across the Internet via other means, and be uploaded by people from other regions once they get their hand on them. Some mapmakers do, however, have multiple SC2 accounts in different regions, which facilitate the spreading of the maps they make across all these regions. So based on that, there is a very good chance that the difference in map availability is minimal across regions.

Also, with the exception of SEA (Southeast Asia + AusNZ) accounts, each copy of Starcraft is restricted to the region it's purchased in. See here for confirmation. UPDATE: That being said, however, Blizzard is looking to introduce Global Play in a future update, which will allow players to create characters and play with their friends from different regions (thanks RamHound!)

Solution 2:

Since you're from EU, you'll have better latency to the EU players. Unless you specifically wanted to play with friends from NA, it would be wise to play on EU. You're unlikely to ever have serious trouble finding a game on either server. Most of the popular maps have distributors on each server.