Thermofoil also know as RTF is a vinyl like coating that is applied to a Medium Density Board door.

It boils down to, "to each there own", I personally like a species of wood, as well my brother in law had his thermofoil doors about 6 month before he got his for chip and they're not a heavy usage kitchen. Then again, I know other others that have had there tnermofoil kitchen cabinets for a couple years and no issues.

MDF can also be painted so the two don't always go together.

You can get slab doors in MDF with real wood veneer. These will not warp. This is what I have. I am in Florida (lots of humidity) so solid wood doors make no sense.