Doctor Who Fans: Choose One

[KiaKat]

I went with the screwdriver.

In my family, I've got two engineers, a (medical) doctor, three computer scientists, and if I'd gone on the other path, I'd be a physicist. Cobbling together a replacement battery shouldn't be difficult. Plus I could use it to create more like it, and wouldn't that be brilliant!

[El Pollo Guerrera]

Going against the usual... I picked the Perception Filter.

Of course, I'd use it for evil... Imagine the security guards trying to explain why no one noticed a guy in a gorilla suit walk out of the bank with an armload of cash, yet turn up in living colour on the camera footage.

[Kal]

Difficult, but it'd be the psychic paper in the end. The uses would be almost infinite (well, probably not infinite but there's a lot of them).
The perception filter would only lead to some villainous sort repeatedly wandering into jewellery stores, electronic retailers or banks with a large sack marked "swag" then leaving with it bulging. The striped jumper, wool hat and black mask kind of go without saying.
As for the sonic screwdriver, given my track record of losing or breaking electronics... Yep, probably not a long term investment anyway.

[Jester]

I would absolutely prefer the screwdriver, hands down, but the fact that its battery life is limited and I would have no way to recharge it forced me to select the psychic paper. Given the chance to get a sonic screwdriver with a recharger, however, and my choice would instantly change.

[XCashier]

Sonic screwdriver, I'd figure out a way to either reverse engineer it after it died, or have an alternative form of power for it.

Exactly. I'm sure the Doctor has some sort of Sonic Screwdriver recharger on the TARDIS. He probably has several Sonic Screwdrivers, so he has a fully-charged one when he needs it.

[cinema guy]

Sonic screwdriver. The original, back before it was a super-duper do everything gizmo - back when Patrick Troughton used it to unscrew things.