I like the backward method because the generator is naturally Low Z and a scope or lightly coupled receiver is naturally high Z. So I hook the gen to the output and scope to the grid.
Most vintage service grade signal generators are a completely unknown output impedance and with most attempting to offer some sort of match into 300 Ohm and higher receivers. The impedance varies widely (wildly with some into the 1000 Ohm + range) with frequency. With those driving forward into the amp minimizes or eliminates the issue.
Carl
KM1H