Per USA off-site data, taller bigs should be trained in 1v1G because it trains HA quicker on the bigs and IS actually trains slower the taller the player is.
1v1F trains IS quicker for shorter guys.
So as a result, it is better to train 1v1F for guards ( typically 6'4" and shorter) and 1v1G for bigs (6'11" and taller). For guys between 6'5" and 6'10" I think 1v1F would probably be fine.