With the "Similar sized display ads" option set ON, I used to have 300x600 , 300x250, 160x600 and 120x600 ads, in my Large Skycraper ad slot (300x600).

However, since one month, I noticed that the only alternative size being used is 160x600 , and no more the 300x250 at all. Do you observe the same ? May be it's to avoid too much blank space?

Personally I prefer the 300x250 creatives, I find the "square" shape being more interesting and appealing. However, I am using the 300x600 because it had a better EPC.

So I wouldn't mind since 300x600 has a higher EPC, however, with the disappearing of the 300x250 ads from it, I ran a little A/B testing, displaying alternatively a 300x600 and a 300x250 ad slot, and after a week, the 300x250 has a higher EPC than the 300x600 one. (by 25% roughly). So it's letting me think that 300x250 creatives are paying more in average, than the 300x600 + 160x600 ones...

So I am puzzled as if I should move back to the 300x250 ad slot or not.

And if I replace my 300x600 by a responsive ad, with the maximum width blocked to 300, will Adsense starts serving 300x250 in it ?