You can have oil leaking past the piston rings and still get good compression, strangely enough. Oil leaking past the rings shows up mostly at high RPM, though the worse the leak, the lower the RPM required to see smoke.
If you have enough compression blow-by, it can force oil back up through the valve cover breather into the intake.
A stuck PCV valve could pull an excessive amount of crank case air into the intake manifold, picking up oil along with it.
As ludesrv said, bad valve stem seals would primarily give you smoke at startup, though a bad enough leak could give you constant smoke.
An oil leak from the head gasket would result in oil on the exterior of the block, or in the coolant. There's no place on the gasket where an oil passage is next to a piston, so you would end up burning coolant, not oil.