Paint vs polyurethane durability
Polyurethane is basically liquid plastic. It forms a hard shell, which will protect the wood underneath. Since pine is considered to be a soft wood, the poly will add some impact resistance. The poly itself may chip, but the wood underneath will be better protected than regular latex paint.

I wouldn't be too concerned about the durability difference between paint and polyurethane. They are both quite durable, and should last roughly around the same amount of time.

The thing with woodwork is that once it is painted, it will always be painted. If the wood is nice enough to be stained, then I would go this route.