Out of these three rifles, I’d have to go with the SKS by preference. SVT40 has a harsh recoil and complex disassembly, K31 has an awkward safety and the paper/foil clips have to be oriented in a specific way for loading. SKS, at least compared to the other two, comes across as a more modern and ergonomic weapon.
As you can see from the patch, Suarez training is well regarded by the Swiss. Several people spoke well of his teaching style and doctrines.