[Polar742]

My personal opinion is that it's a matter of brakes and steering.

In my experience you always start the engine (on twins) that supports the nosewheel steering.

FWIW, on the 747, we taxi out on 1&4 as that supplies the brakes and steering.

In any case, you have an engine driven pump, and your back up pump to support the steering and braking. Were you to start other combinations, you are using your backup pump to operate the system. If that fails, you're filling out paperwork.