Seriously, though, I can only speak for two of those so far, but they're quite different. Karlskoga feels more like a rallycross track than a "full blown" racetrack, it's quite narrow and twisting (so overtaking is quite hard) and it also feels smaller than it actually is. Mantorp, on the other hand, feels more like a "proper" race circuit and also has that huge wide long back straight and more opportunities for overtaking.
So between the two, it really mostly depends on what you're after.
Can't talk about Anderstorp as I don't have it just yet.