I don't know if there is a "best" caliber to patch, but I lean toward the big bores. When used for hunting, small caliber lead bullets tend to kill differently than their jacketed counterparts. Because of the velocity, the bullets are generally hard and break, sending fragmentation and small pieces outward from the wound channel. By patching, you can drive a heavy, soft bullet that expands and has enough mass to give deep penetration. 405 grains penetrate better than 170 grains, especially if flattened out. Besides, it's much easier for me to handle a 45 caliber bullet than a 30 caliber one, although both will work when cast of soft lead and patched.