I first got final blitzkrieg, I really love the era but the only features it has that CMBN doesn't are tank riders and more modern weapons I think. I couldn't resist and had to buy the Normandy + commonwealth bundle and the quality is the same due to the V4 update and I haven't been let down. With both games the battles you can have is endless and I can guarantee you will enjoy it too. It's your choice so get which one appeals to you more. Personally FB is more open with less cover available due to most of the fighting being in the Ardennes region whereas CMBN is different as there is more cover due to hedgerows.
Theyre both amazing games so good luck in deciding which one you want!