Monero’s strength is privacy not spending imo— especially since exchanges have begun delisting it. But even if you were to say bitcoin spending and privacy is poor, there are solutions in the works for both, eg lightning, mimblewimble, coinjoin, fedi, those ecash nut things I think. 

If one agrees both have similar function, I’d go with the one that is auditable (bitcoin) and has the largest network effect (bitcoin), personally.