I think that all of the firearms in question are virtually the same. Furthermore, I may be mistaken, but I think that the AK 47 and all it's derivitives are 7.62 X 39, while the AK 74 and it's derivitives are the russian 5.56 ammunition. I have been told that this 5.56 ammo is slightly smaller than 5.56 NATO, so that if the soldiers carrying the AK ran out of ammo, they could load captured M-16 bullets into their mags and shoot them.
Well, as far as comparisons go, I'm not really for sure about all these pics. I know that the AK family is so diverse that it is hard to tell different variants appart. In addition, they are very customizable so an original AK 47 can be fitted with all kinds of accessories to function better or just to look like a different version.
Like I said, I don't know everything about AK's, and with all the types out these days it's hard to tell. I'd venture to say that the AK SU's are virtually the same, save for a few different modifications (flash suppressor, stock, etc.)