It's a tossup between the DataDyne building, Pelagic II, and the Carrington Institute. I like the DataDyne building because it's cool and creative and there are 3 missions in it under three different contexts, but the level itself doesn't have enough variation and alternate ways through it as I would have hoped. Carrington institute is good too, but in some ways it's too big, which would not be a bad thing if only the level made use of more of it and it wasn't so hard. The Pelagic II is a good map as well, but then again, a lot of it is very similar and there isn't a whole incredibly lot to do in it. But overall, if I had to pick one out of the three, I'd probably go with Pelagic II.