For me, it all depends on what the puzzle will be used for. If it is just going to be used as a decoration, then fine, I will use pine, poplar, or any other kind of wood. If the puzzle is to be used by a small kid, then I use baltic birch. I use the BB because it's so durable, it hardly ever breaks, not even the tabs. No matter what type of wood you use, there's always a chance of it breaking especially where the wood is thin in areas. I always sand the BB before I glue the pattern on, and when I'm done cutting the puzzle out, I remove the pattern paper with after-wash. It's the same as paint thinner, and it removes every bit of glue residue. After all of the glue residue is removed, then I can use whatever I want for a finish.
Len