For the two-player base game, my opinion is Boston to Miami (12), Dallas to New York (11), and Chicago to Santa Fe (9).
- Boston to Miami (12) + Dallas to New York (11): For these tickets, the point values are high enough to hurt if ignored and low enough to be beaten by many other combos, especially since you'll need to place many short routes and hope the game doesn't end too early. Since no other tickets use Dallas or Boston, they are also easier to guess (and block) than most other combinations. This is the worst starting pair I could come up with.
- Boston to Miami (12) + Chicago to Santa Fe (9): Many of the same problems, but you might be able to ignore Boston to Miami (12) and place down 6-orange, 4-green, 6-black, etc. This could trick your opponent into thinking you have Los Angeles to New York (21), Los Angeles to Chicago (16), Denver to Pittsburgh (11), or another suitable ticket, which you might actually get if you draw more tickets.
- Dallas to New York (11) + Chicago to Santa Fe (9): You can complete both tickets while bluffing Los Angeles to New York (21) + Los Angeles to Chicago (16), but eventually you'll have to spend a few turns to get to Santa Fe and Dallas.