Please note: UA miles currently can not be used for upgrading on SQ flights. The new *A upgrade awards using UA miles are still restricted to certain *A member, such as LH, NH, or TG.
DL miles can be used for upgrade on UA, but I think it has to between Asia and North America, or FRA-JFK. Plus the ticket has to be issued by DL.
I don't know about using US miles. Perhaps you can look up the respective forum.