You must have had some horribly bad piston-single autopilots then, that's unfortunate. By contrast I've never flown a plane where the autopilot WASN'T capable of being trusted, and I've only flown piston singles.
The way I see it is if your autopilot sucks that bad that you can't trust it, fix it or remove it..or if it's a training issue, go get training on it. If it's in the plane and it will help lessen my workload, improve awareness or generally make things easier, I'm using it.
Don't they teach you the perils of being MACHO in commercial training?
I do what a few other people have mentioned, hand-fly for proficiency and practice, but to make sure I keep practice with automation, I let the autopilot fly some approaches.
My autopilot is not coupled to the glideslope so I STILL have to pay attention there, but it will hold a loc needle well.