As a prior post noted there is little to purchase at MTR, but if you pass through late summer the hiker barrels are a virtual cornucopia of food stuffs. A late summer hiker can probably scrouge better than they can think to pack a resupply.
Okay, that said, MTR is a bit further along the trail than VVR and if you do not plan another resupply before Whitney Portal I'd recommend using MTR.
And that said, if you have time, make the stop at VVR as well. The restaurant, shower, laundry, and the possibility of a bed makes VVR well worth the 1/2 detour. And an added bonus of breaking bread with a dozen or more fellow JMT through hikers, encouragement of one another and the comraderie that you will thencefore share with most of them for the remainder of your hike.