Yak paddles make too much noise for my taste. My 3 minute trial with one got me wet enough to just say no thanks.

If you don't mind switching, switch. It's probably the most efficient, other than the switching part. I end up doing that if paddling into a hard wind or if I want to go fast. Going fast isn't efficient IMO, just more work.

A C as described works ok. So does feathering. If you have long arms and can get the blade under the boat there's much less correction needed. I can do that at a speed I consider efficient all day but if I try to push it speed wise, even a little, the back of the boat starts skidding out and I have to rudder it back. Remember it's called a paddle, not a rudder. Ruddering is for turning while slowing down like when you're coming up to a landing.

If I had a solo boat of my own, I swear I'd take out the seat and move a thwart to position the seat back as far as I could. Paddling at the middle of a canoe has always seemed dumb to me. I hate switching.