I did 6-50 because I plan on HPWC. Both the 6-50 and the HPWC require only 3 wires whereas the 14-50 requires 4 wires. So it's cheaper to run a 6-50. You'd need the 6-50 adapter of course.
For shorter runs, it doesn't save that much (though does reduce the size of the required conduit). Something to the tune of a buck a foot.