I have used the list below a few times with varying degrees of success and was looking to tweak it a bit to make it more effective. The first thing I was going to do is replace the Stealth Devices with Hull Upgrades on the Defenders. I don't seem to get much mileage out of the Stealth Devices and a Hull would be more dependable. Any other thoughts?

Darth Vader in the TIE/x1 with Predator, Twin Ion Engine Mk II, and Advanced Targeting Computer (34 points)

Delta Squadron Pilot with Stealth Device (now Hull Upgrade) x2 (33 points each)

I think your change is a good one and makes perfect sense. Stealth is really only good on a ship that can get multiple defensive tokens to help mitigate a bad roll.

Ultimately though, TIE Defenders are not easy to be successful with. The hull does help them stick around longer, and if you can use one for blocking (the one that's taken damage), you might be able to deal some damage with the other two. Another problem in this list is engineless Vader---he can't k-turn endlessly along with the defenders and if he dies your defenders could struggle against higher PS arc-dodgers (unless you can block them).

Having said that you should probably try the list with the hull upgrades and see how you like it. If you still want to make a change, you could either drop Vader or drop the defenders. If you want to drop Vader, I would consider Carnor Jax in his place. Gear him up with Push the limit, royal guard title, autothrusters and hull upgrade. Fly him conservatively either on a flank or behind the defenders. Try to get him behind the enemy at Range1 and once there, try to keep him as close to the enemy as possible so that his ability can deny your opponent their focus and evade tokens. This will increase your squad's firepower and survivability at the same time...

Alternatively, if you were considering ditching the TIE defenders, here's a list that I've had a lot of fun and some success with that includes Vader. Its also kind of cool running a pair of royal guards as Vader's escort:

Darth Vader w/ lone wolf, x-1 title, ATC, engine upgrade & proton rockets = 39

2 Royal Guards w/ push the limit, royal guard title, autothrusters & hull upgrade = 30 x 2

99

You could trade the proton rockets for an ion pulse missile. While the proton rockets add a slight damage buff, it tends to be only +1 damage which you may or may not need (I like it personally, although its not always necessary). The ion pulse missile would be handy against large-based ships, so if you see those a lot, its worth considering. This is not an easy list to fly though, so some practice would be good. The main problem is keeping Vader away from the escorts so that Lone Wolf stays active as much as possible. I really like Lone Wolf on Vader because without it, he's a bit squishier than I'd like. That 1 re-roll comes up more than you might think, and has always been worth the 2pt investment for me.

In my recent matches the Defenders have been the real workhorses for me. Part of that has to do with me flying Vader like a drunken sailor, bu the other part is that I have been able to get them into positions where they do some real damage. They are tough enough to not be one-shotted and have enough damage output to bring some pain.