My favorite bow is a shorty made of eucalyptus, and it is stiff. I like the eucalyptus for its fibrous lateral strength...
My flex bows generally have thinner cordage and my stiff ones have thicker. I see some relation between the size and stiffness of the bow and the cordage thickness. I have a great little Osage Orange flex with some thinner cordage and she loves working the spindle!
On thinner cordage, like the jute pictured above, I personally would use one with a little more flex as thinner gauge cordage with stiffer bows seemed to wear through the cordage more, from my experience....
But I would also recommend going two-ply or four-ply...
Doc is correct, not a large difference between a larger bow and a shorter one - if you know the technique... Notice Doc's 'Egyptian' technique requires a good amount of cordage, more wrapping and thus a stronger bow is required to do the motion. But the motion, even for a smaller bow, concentrates the energy well - again if you know what your doing... With as much cordage used in the 'Egyptian' technique, you might as well carry a larger backup bow and spindle to compare results...
I generally advise those just starting out to use longer bows before going smaller. This emphasizes more on the technique, speed, and stroke. Moving to a smaller one once this is understood. The technique is somewhat different between the larger and smaller. But it may be different for others... If you want to go all-out practice the technique on green wood.
My first bow was tiny. A little compact handheld. The way I learned was with fresh, green willow. This was the way my teachers wanted. I worked that green willow for over a week. This was to emphasize on technique, not fire. On the fifth day I got smoke. By the end I got a faint coal. The willow started off green, but was heat seasoned over time. As I perfected my technique, the wood was being prepped. Finally, when I got it down, the wood was ready for a coal. I didn't get a fire however.
I moved on to larger bows and spindles. A different style was used which was calmer. I paced myself more, less explosive, quick 'rabbit-sex' energy, if you will. More surface area on the spindle/hearthboard, allowed by a larger bow, and I had a hearty coal and fire. As I perfected the tinder/coal/blow/fire aspect, I then went for a happy medium between the two sizes until I found my optimum. I played with cordage types all the way. A thin double ply of dogbane snapping on a dark, cold night taught me the value of thick ply cordage and 550 paracord backup. And of the hand drill.
I only use hand-drill now, as it is more quickly made out in the field and less cordage waste. It is my preferred method, and the method I wish I was taught first. I teach all my students hand-drill first, and then bow-drill. They agree the hand drill is much easier. In groups of three, 100% success the first time. 6 year olds included!
I carry both a bow drill and ferro rod backup in my fire kit.
But what we can take from this is, try it all! See which combination works for you and which doesn't! First, however, work on technique honing and local material (woods, cordages) gathering and use...
, I find it somewhat hypocritical of you to cast aspersions on Mr. Magnussen due to the presence of the beer bottle when you completely ignored the bottle of Bailey's at the left bottom corner of the first picture. For your congratulatory toast at being a first-time friction fire maker, IIRC?
