I think Mike has summed it up very well. Over the years I have used a scroll saw I have found that some machines seem to like certain blades depending on speed, tension, type of wood used etc. In general I favor spirals for portraits, number 5's as my main flat blade for general wood thickness, with 7's and higher for thick wood. If you look at Olson's chart you'll see that they recommend certain TPI [teeth-per-inch] for various woods, plywood and MDF etc. The TPI is a moveable recommendation to any sort of blade. What makes the difference is how various blades -- Olson, Flying Dutchman etc -- are manufactured. It's a bit like fans arguing Ford v Chrysler, Canon v Nikon etc if you get my drift. It comes down to what you find best suits you. Hope this helps. Magic