I don't know if they are the worst or not, but I've had really poor luck hunting Quail. They are really good at hiding, then breaking cover right under my feet with a rush of whistling wings, that shocks me more often than not, even though I'm expecting it. Kind of like a Quail grenade going off.
Jack Rabbits can be fun, especially in the high desert where clumps of brush grow with open spaces between the clumps. When the Jacks bed down mid morning. you can kick the brush clumps and every so often a Jack comes busting out at full speed. They come out in any random direction, take three bounds and change direction, then do it again and again. You almost have to anticipate which direction they are going next and lead them some. It takes really good reflexes and instinct aiming to get any hits. I've had some fun times Jack hunting. And actually Jacks are pretty good eating, no much meat on them, but what is there is tasty.