I always use 128x128.

128x128 for me
i hand draw heads/sets, but i find i dont need any more room to make great heads/sets
though 256x or 512x may give you more room (especially when doing things by hand) the quality loss really dissapoints me :/

also, i find 512x to be too big to work in (dont kno why, jus me i guess)

4x more for 256x256 is fine with me
I use 256x256
However, in my new style, it's not all drawn in with an airbrush, so I go for 512x512.
That's just in the trails.
Heads, which will require drawing in each shadow by hand, will be in 256x256, since 512x512 requires way too much time to make.

Really, 256x256 is sharp enough for anything that will still look good on a toi scale.

Right now, the added bonus of buying 512x512 is that you can load them yourself into a customs folder and enjoy spectacular quality, just gotta make the folder locked, so the update server doesn't overwrite it.

What loses the most quality when being resized isn't the style that idealizes the textures, with shiney robotics, or glossy looks, but those that add the worn out look, with scratches and small scuff marks.

This discussion has been had before.

Nice that you made a poll though
The options are a bit overdone....