The odds of you having to make that decision are very slim.

Since none of the domiciles for either airline are near SAT (LAS is closest) I would look at the major hubs (VX: SFO, LAX, JFK) (NKS: DTW, LAS) and check out flight schedules to SAT.

I would guess LAS is the best bet, since it closes and service from multiple airlines

But this is not a dilemma you are likely to actually have, and there may be other factors aside from commuting to consider.