Since I am painting all my trim, I am using MDF instead of wood. I have used it before...it's great! Not so good for bathrooms or around the kitchen window (places where it gets wet a lot). It is cheaper than wood moulding, it comes in 14' lengths (so there is less waste and less seaming) and it is preprimed so getting a nice finish coat of paint is much easier.

We also used a preprimed MDF molding. It is a lot less expensive than wood and you can't tell the difference. We matched new molding that we put in our family room, we will eventually put throughout the whole 1st floor.

Also if you are DIY'ing any crown molding, we highly recommend cutncrown tools! Being amateurs, we have used them for all our crown and it takes the guesswork out of how to cut it. We went through about $100 of crown that we cut wrong before we used the cutncrown and got it right the first time.

Good luck!

Here is a link that might be useful: CutnCrown