I' d say go with the heavier of the two, just based on principle. Really though, 21 grains simply is not going to make any difference whatsoever. Neither arrow will be more ' forgiving' than the other. KE and momentum will be practically identical.

If one was 390 grains and the other was 490 grains, then we' d have something to discuss.

There is no choice to be made between those two arrows on any criteria except which arrow shoots your broadheads with more consistent accuracy.