The Personalize Your Sonic Screwdriver set and the Trans-Temporal Sonic Screwdriver. I don't know exactly how many combination possibilities there are, but it is quite a few.
I'm only doing the emitter switch. I like the Trans-Temporal emitter on the full body of the second screwdriver
*insert Sonic Screwdriver sound effect here*
Jeez, I'm actually really jealous of you right now. XD
I would do the head of 1, the body of 4, the handle of 2 and the bottom of either 1 or 4 (going left to right that is) Congrats on having all those sonic screwdrivers!
the head of 4,body of 3, handle of 1,bottom of 3.
I want to do the head of 3, body of 4, handle of 1 and bottom of 4. I think it would be a cool, steampunky screwdriver
256 combinations! Lucky you