More than likely Sony is probably going to have more units. Given what we know MS probably is probably going to have a bigger chip which means Sony will have a yield and chip volume advantage per wafer.
And Sony is a CE company who launches way more hardware products than once ever 4-8 years. This is where Sony should have a definitive advantage here.
Unless Sony has lost its touch, I can't imagine MS having more units.
The GDDR5 vs DDR3 situation can easily cancel out all the above. We dont know.
PS4 is much harder to get a preorder on in the USA where I live, that much I know. Whether it's supply or demand isn't something I can see.
PS4 preorders are sold out everywhere but you can still preorder stand alone Day 1 Xbox at at least two online chains (Best Buy and Microsoft Store). Also XB1 bundles still available at Gamestop a few days ago, etc.