A long long time ago, I was taught this method, and I believe it is the correct method that puts the least possible stress on the drivetrain when parked on inclines:
- Drive the vehicle into position, and bring it to a complete stop with the foot brake
- Hold the vehicle in position with the foot brake, and put the transmission into Neutral/N
- Apply the parking brake just tight enough that it feels like the vehicle will not roll/creep
- Carefully lift your foot off of the foot brake, paying attention to whether or not the vehicle does start to move at all
- If you detect any roll/creep, apply the foot brake fully again, and tighten the parking brake another notch or two as necessary
- Once the vehicle is completely held completely still with the parking brake tight and no foot brake applied, put the transmission into either Park or 1st gear.
This way, the weight of the vehicle is resting on the parking brake. That's why you have a "parking" brake. Putting the transmission into Park or 1st gear is a safety backup, so that if the parking brake was to fail (such as the cable snapping), the transmission will prevent movement of the vehicle.
Take care of your transmission and it will last a long time. The parking brake is a simple mechanism with a cable and brake shoe that is cheap to replace and generally easy to work on. Use the parking brake.
I especially hate to see drivers throw their truck into a forward drive gear while the truck is rolling backwards, or vice versa, or throwing it into Park while the truck is still moving. Such sloppy driving really decreases the life of your drivetrain.