No. Neither will mean anything to anyone. Tell the CM what you
need in relation to the attractions. You don't have to get a GAC the instant you enter a park; you can tour for a while, or a day, and see what your needs are.
If your needs are [primarily] mobility or stamina related, Walt Disney World's recommendation is to rent a wheelchair or
ECV. Do you, currently, foresee any need other than getting the moving walkways slowed? If you don't, then really it makes sense to wait until you try some attractions before getting a GAC unless you do choose to use a wheelchair or ECV; then you'd probably only need one if you have other needs. Slowing a moving walkway can be verbally requested if not automatically offered EXCEPT it CAN'T be done at Peter Pan or Tomorrowland Transit Authority.