What is your best interdictor build and what would you run with it?

What do you want to use it for, that's the key to what's best. You can make an absolute beast of a repair tank with interdictor, wulf, engineering teams/projection experts (your choice) and targeting scrambler. However it can't hurt anything, at all.

you can make a passable attack craft with engine techs, wulf, high capacity ion turbines and disposable capacitors, but then why are you taking an interdictor when you could take an ISD for about the same points?

To me, the best Interdictor build goes all out for objectives and is super defensive. Grav Shift Reroute is 2 points that can earn you a ton back on Contested Outpost, Station Assault, and Salvage Run. Make it a full Interdoctor with Wulff Yularen, Projection Experts, and Targeting Scramblers. The rest of the fleet is big lumbering beasts like VSDs with some of the new buff upgrades. You dare the enemy to fly into your teeth, because otherwise you score easy objective points and win.

Your opponent can still win if he's very clever and outplays you, but that's true of every fleet. If you like defensive play, and not everyone does, then this can work.

Suppression/Tua/ECM/HIgh Capacity Ion Turbines/Grav Shift/Grav Well.

Distinct effects on opening of game. BBBBR side arc does a good chunk of damage.