I'd say it's a toss up between Amtrak, airlines, and whatever bus company decides to start a Midtown-Crystal City route. I think everyone is overhyping HQ2 though. This is not something that alone is going to garner enough ridership for a whole new train service or air service or whatever, but it adds nicely to the existing portfolio of potential customers. Regarding travel between HQs, are people who have to travel going to go from office to office, or will they go from home to office? That's going to be a huge factor in what mode they take. For Amtrak to win out overall, I'd say Amtrak is going to need to add Crystal City to its Virginia trains. HQ2s location in LIC is nowhere convenient for an Amtrak/LIRR station unless a new tunnel was built to get NYP tracks 1-4 onto the island with an underground stop in LIC, and that's a VERY long ways away if it were to ever be remotely considered (and that's still a bit of a hike to Anabel Basin).