I use 50/50 because I make most of my recipes 50/50. A lot of people like to maximize their VG, so for them VG-based is better. Some people are sensitive to VG or PG, and would obviously prefer to limit their exposure, and choose that way.
Most flavor concentrates are PG based, so if you are using, say, a 10% flavor percentage, that's (usually) going to be 10% PG in your mix right off the top, so one reason to use VG nic base would be to offset some of that PG (if that's your preference).
As a general rule, PG is better for flavor delivery, and VG is better for cloud production. Usually retail juices for subohmer / high wattage / cloud chasers are high VG.
So it all just depends on how you
vape and what you like.