Buy the Express Pass tickets. When you get to the building itself (or the website) you'll wonder, just as I did, whether the extra cost (over double the price) is worth it.
Speaking as someone who opted not to get the Express Pass take my word for it: the extra expense is worth it. The Express Pass allows you to skip all the lines. When you first enter the building you'll go through security and that will make you think all the lines will be quick going. I will say that the staff at the ESB gets a lot of people moving quickly, but you're still going to be waiting for at least an hour without the Express Pass. Buy it (and don't get the map. You don't need it).