I would say Computerwelt, as it is really accessible, very light compared to a lot of their other work without becoming drab. Tour de France Soundtrack could work for a starting point as well, but it's even more light-hearted and may not be a good indicator of the albums that precede it. Most people tout either Autobahn or Trans Europa Express as both their best starting point and their best work overall, but in both cases the albums are largely defined by their centerpiece tracks. Die Mensch Maschine is the most cohesive from start to finish, though; I think the DLA really nailed it by holding it above the rest of their albums.