After testing tons of variations and completing the campaign myself, I strongly believe that
Dead Ringer with Specters is by far Vex's best leveling build. The Specters are significantly stronger than I expected, they are powerful minions with guns that absolutely BEAM everything and their damage scales off of any gun damage increases you get, so they feel really good. They are incredibly consistent, and don't require much point investment. As a result, we can optimize our points to get as much damage as possible, mainly dipping into both the blue and green tree for consistent high dps output, taking advantage of the strongest nodes from both trees since it's not efficient to go for capstones at such a low skill point budget.
Be on the lookout for a throwing knife with the Penetrator Augment as that will guarantee any of your shots to be a crit, making
Bloodletter incredibly powerful, especially on boss encounters. If you want to use
Bloodletter regardless feel free, I just don't take points into it because for leveling you ideally want to 1 shot anything that comes in your way, and a DoT effect isn't usually the best at low levels without a ton of scaling. It's also crit reliant which may not be great depending on what gun you happen to get while leveling.
Endgame version here
Previously this leveling build was focused around
Incarnate, however after playing the game myself and finishing the campaign now (as I didn't have early access) I've come to the conclusion that
Dead Ringer with Specter minions is ultimately much stronger when you are very low level and lack skill points. The previous build can be found here but this build is better for the above reasons

























