The 14-50 has 2 equaly sized hot contacts, the 6-50 has one smaller and one larger, but they are both rated for 50A
If you price out 6/2 NM vs. 6/3 NM you will see the difference in cost
A 14-50 can also be used by a visiting RV, while a 6-50 can be used by a visiting welder
Whatever you decide, I would still own the 14-50 adapter for on the road charging, that is the most popular 50A outlet, which was the original question
I own
all if the UMC adapters, and I have built cords to other outlets as well (10-30R to L6-30P, L6-30R to L6-20P then I have my "Quick 220" I built that has an L6-20R on it, so I can hook it all together (using a Tesla 10-30 UMC adapter) and use 2 out of phase 120V non-GFCI outlets as well (you dial down the current to 12A)