I can't imagine they'd force you to take that bus -- if you're willing to wait for the next one, however long it takes, I suspect they'd allow you to do so. (If you have a medical issue that is the reason for wanting to be in front -- you might simply explain it to the driver or to the people in the front seats and see if they're willing to let you have them.)
Wherever you find yourself sitting, the buses are not cramped, and the comfort, view and space are good no matter where you sit.