I have both French and Satin, and I like both breeds. I think they each have their ups and downs.
French are certainly huge fiber producers, but so can most Angora breeds be if you get into the right lines. I was slightly disappointed with my oldest doe for producing only 5.5 ounces this molt, but that's still a good harvest when it's usually estimated that they give only a pound a year. Also, well socialized French are usually comparable in temperament to a giant pillow. As far as fiber texture thy are supposed to be a coarser wooled rabbit, and if you have sensitive skin, the guard hairs that create the halo can irritate you. As far as size, I have oversized lines that finish out between 11-13 pounds usually, and though it's too large for show, I just processed some Jr's that I bet were at 5 pounds at 11 weeks, which is pretty impressive for also having to grow all that wool.
As far as satins, I'm still fairly new to the breed. The coat is so silky soft and shiny, but they do produce less and I feel like they mat easier, though admittedly the mats are also easier to remove with how slick the wool is. The three adult rabbits I have are from two different breeders, and they were well socialized, so the temperament is very similar to French, the only exception being that they don't stay still when you go to pick them up. They do try to get away, but once you have a solid grasp on them they settle down. Otherwise, they also come to the door for pets, take treats from your hands and sit well on the grooming table. No crazy tendencies to fly off the grooming table or to bite or anything stupid. I think temperament is more based on lines and how they're handled when young. I am surprised by how small they are though. The largest doe is only just over 7 pounds, but they are compact little rabbits, so if meat is an option further down the road they wouldn't be useless, just smaller.
As far as spinning, I enjoy spinning Satin and French pretty much equally, so I feel like it doesn't much matter there. Although I will say if your after that pretty sheen in the Satin coat you may stay away from certain colors like black at the start. Like I said I'm just starting, and though I can see the sheen of the fiber amazingly well on my REW, and pretty well on my chocolate chin and her chocolate kit, I can't see if at all on my black bucks, though I've been told my breeding buck has nice sheen. It looks almost the same as French to me, just softer coated.