Is one in a shadier spot?

Oaks often produce leaves in shade that are more shallowly lobed than in full sun. Also, seedling oaks often have leaves that look somewhat different than adult trees would.

Although the shape of the left side isn't "classic" Nuttall Oak, I have seen them look like that, and the reddish new growth is also typical of Nuttall (and others, to be fair, but esp. Nuttall).

What hairmetal said, the left one is that a baby? It could be a hybrid also, but, I would wait til it gets bigger.
I must admit the left one looks like Q. Rubra or Q. Velutina also. But I must admit oak leaves confuse me when the aren't exactly as the field guides depict.

The one on the left is actually older. It had been headed back several times in the nursery (to keep the size down I guess) so will take a bit of pruning to get back to a good leader. Not sure if it was kept in the shade or not but it is in full sun now so we can see if it looks different next spring.

Here's a follow-up in case anyone is curious. The late season growth between both trees looks very similar. Perhaps it was a case of different conditions in the nursery after all.

Mosquitogang, It's great that you have a real answer to your question. Oaks are sometimes very hard to figure out when it comes to leaf shape. I ordered an oak online which showed the leaf shape of the adult tree. Quercus Sinuata, from Mossy oak natives nursery. It is also called Durand oak or Bast**d white oak. The tree online had lobes, but the tree I received and planted had no lobes, and had Willow oak shaped leaves, which stayed on the tree in the winter of 2012-2013, which was a milder winter than the last one, 2013-2014. Well, anyway, I have a Nuttall's oak that has (usually) nice bright red leaves for fall, and once shed, the spring leaves are nice and bright red for a while etc. The other Nuttall's oaks I have don't have as showy leaves as this particular tree. But really, I must admit this year this usually showy Nuttall's oak hasn't been too showy, likely not enough of a cold snap at the right time or who knows the reason?

Grew out some Nutall seedlings from acorns this year - several would easily have passed - at least early on - for Q.nigra seedlings - and I even considered the possibility that they could be hybrids of the two species, but as subsequent flushes of leaves came on, they began to resemble, more and more, Q.nutalli.