You should really use 3 since obviously people want a bit more than 2 and a bit less than 4. I use 3 for that reason, as I was most productive at 3. At 2 I don't get an overview easily enough, at 4 indents start to creep too far out making it hard to work in larger functions. 3 is really the smallest number where I still easily saw the big picture structure of a file, so I feel that is the optimal one, at 2 I start to not be able to eyeball how indented a piece of code is.

Not sure why people are so obsessed with having power of 2 spaces, can anyone explain that? Why argue over 2 vs 4 when you can have 3 for everything? I think 4 is better than 2 since 2 is too hard to track, but 3 obviously is better than 4.