I love economic games that play in < 2.5 hours.
I own the following train games:
1) Steam - love it and want to try the advanced rules to get a more AoS flavor, a game I've not yet played.
2) Chicago Express w/ expansion - love it. I've played this game the most (about 20 times), and it's easy to teach and get players in. I've not played much w/ the expansion b/c everyone is having fun w/ the base game.
3) American Rails - just picked this up and I'm itching to play! I'm going to buy some illustration board and mount my board like a fellow BGG'r did!
On one hand, Germany Railways gets the nod due to better component quality. On the other hand, Pampas has received strong reviews, and I'm more on gameplay anyway.
My major concern is, with either of the two games, am I getting too much of an overlap to what I already have? Seeing how infrequent the games come to the table, do I really want a game so similar to what I own? Note: I see similarities to American Rails with C.E., but I think they're different enough to have both.