I have the APO, and even mark will agree that it is best to go with APO rather than non, just because the APO sorts out certain problems that arose with the original. I wouldn't buy the Nikon G-mount, doesn't get great reviews. I like the Sigma, and it is a good lens for cheap, which never underperforms for me.
For examples, see (I dunno if I gave you these already, or if mods will permit):
This
and all most of the ones at the beginning (almost all of them):
Here
HTH
Jack M