Is MDF a reliable product for interior trimwork?
Mdf is a fair product for the price.
I always advise clients to choose real wood if the budget allows. As to what you have heard; Mdf in a dry interior environment will not warp like wood. It should not be installed in kitchens, bathrooms or outdoors. A good carpenter can use wood or mdf to provide pleasant finished details. If you can afford it, choose wood.