If you plan to paint it, mdf should be fine, unless the tv is really, really heavy, then I would use wood.

HI -- Actually MDF is wood -- wood fiber/ sawdust mixed with glues and put under presses to form sheet goods . And there are different qualities of fiber boards . M - is for medium and then there is HDF which is a lot stronger - H for Hard which is used for better quality furniture and high end kitchen cabinet doors etc. For a better bookcase you could make the box part out of MDF and then have solid wood or plywood for the shelves . For a good finish on MDF or any wood -- do two or three coats of primer , sanding with fine grade sandpaper between coats , then apply your paint finish.

lefty, I didn't know it came in different qualities! Thanks for the tip!

Not sure if this is the same post as the veneer vs craved MDF one?