256 body, 512 head, if your art is made excellently, honestly you can't really tell the difference until you zoom in :P

I can only see black background on your 256 textures :<

Here is my cartoon set the one on the left is my right leg in 256 and the right picture is my right leg in 512. Like I said when it comes to cartoon it makes nearly no difference, just the text is a bit blurred.

Well it depends on the detail of your set , if it is as clean as simple as mine 256 will do.
For more complex and highly detailed designs i suggest you buy full 512.

As I can see the difference between that legs isn't so big. I think I'll go full 256 + 512 head. Thank you all for your time and help ^^

I really think that 128 tops both of them, they are affordable and I really do not see the difference.

No, 128 is really low quality. But also the most popular.

If your a good artist then it is not that bad quality.

512 is better in every way.
no matter how simple your set.
my set is basically just 1 solid colour shape on a background and i cant stand it in 128.
simple sets need sharp defined lines, and 128 blurs those lines slightly.
a good artist can still make it look good, but it will always be better in 512

Basically what Ben said.

If you want quality then price is meaningless, if you want to be more economical and have just decent quality then 256 is good for you. I would, however, pick 512 over 256 any day.