The Nutball is the slowest I’ve flown. It’s fun to fly it backwards with a moderate headwind. It’s a pretty good plane for tight spaces too because it can turn on a dime. The 2022 Nutball is lighter (and slower) than the original.
For planes with an actual airfoil, probably the Storch, but that’s no good for a yard. I would have thought the Mini Old Fogey would be good, but mine is unstable at low speeds.