For interior decorating purposes MDF is king.  There are many reasons why this is the case.  1. MDF is extremely smooth compared to Baltic Birch or any other wood for that matter.  This makes it much easier to paint and anyone who has painted both knows exactly what I mean.  2. MDF does not warp like Baltic Birch.  Visit your local Home Depot or Lowes and compare the big sheets of plywood to the big sheets of MDF and see for yourself.  3. MDF is 4 or 5 times less expensive than Baltic Birch.  That last bit may help you determine if you are paying too much for your MDF products.