As some of you may already know, the Finns recycled old rifle receivers to build their Mosin Nagants so it depends on whether you mean oldest receiver or oldest in current configuration.
I have an M39 with a 1944 dated barrel built on an 1894 receiver and I also have an M28 (these were made between 1928-33) built on a 1916 receiver.
They are both range queens that shoot pretty well, but I think the M39 is a tiny bit more accurate. However, the M28, being a pretty beat up looking old gun, gets curious looks when I shoot it well.