I personally use vex over thorn

Thorn.. is by far superior to those weapons listed.. vex was at one time the pinnacle of exotic primaries however its has long fallen from its pedestal due to the continued controversy surrounding it, on solar burn it's still a powerful and situational weapon but easily outclassed by Ghorn in those situations and when solar primaries are available such as Vision there really is little need to use it.. mine now sits in the vault collection along with many others Suros is right next to it as well.. at the moment primary exotics save one Hawkmoon have little to no use in PVE and again when Ghorn is so powerful you rarely need to use primary or secondary exotics unless you just want to mees around with them. PVP on the other hand I'd say in order Thorn,TLW,Hawkmoon followed by Reddeath, Bad Juju and then Vex but in a 1v1 mid range encounter you will lose to HC's everytime close to mid you stand a better chance but still likely to be more successful if you swap it out for a HC if you find yourself struggling