2 cycle fuel, 4 cycle fuel. I think it's all marketing. In fact, some fuel makers don't differentiate between the 2 fuels. Use a good quality fuel with nitro and oil mix you feel good about. I personally use Byrons 10% nitro with 18% castor blend in all my glow engines. I have for years, with zero bearing or build-up problems. I don't have any Saitos, or YS's anymore, so I don't really need the higher nitro.
Quality is the most important. I see brands in shops now, I have never heard of. No thanks, I'll pass.