For me it's softwood.
OK, yes, it is affordable and it looks pretty good if you don't get the cheapest crap. But DAMN IT why does it have to have all those knots?!? While you're happily sawing away*, the straight line you managed to follow starting to impress you, you'll invariably get to it - the knothole. It will slow you down, it will require more force to make the saw keep going in that straight line, and if it's your lucky day you'll end up with one big hole in that very visible front you happen to be building right at that moment.
Boy, did need to get that out of my head... do you have anything of similarly utter importance?
*yes I know how stupid that sounds