It depends on what you are trying to accomplish. If there are sharp corners, you may need smaller blades. The wood makes a difference. Feed rate matters, as does how much you are willing to sand. My go-to blade is a Pegas #3 MGT. If that isn't working, I'll switch to something else. I routinely cut 3/4-inch wood with a #3 blade. It is slow but smooth.
Cutting straight takes practice.