500mb and 2gb are the same? I wonder which one should download?
The compressed one has slightly lower quality due to the images which is the big chunk that gets download in the other one.
So if you lack space or do not mind a slightly less "Minor" down grade in graphical look chose "Compressed version"
If you have space enough and do not mind using it, or have a problem with a lightly lower quality images for the game. Use the regular download :)
That is the only difference there should be between them :) I hope it helped a bit.