I use a 6-foot Kryptonite cable with my own armored padlock. Not as heavy as some chain solutions, plus I can usually secure both wheels and still include some firm stationary object.
My seat post height adjustment is not cam-operated, instead requiring a hex wrench, so I don't remove it. But then I never leave my bike unattended for very long in high-crime areas. And I usually manage to be in places where I can keep an eye on my bike often enough to also reduce the theft risk.
Furthermore, I have my bike registered with the local police, with a difficult-to-remove sticker on it. May not prevent its theft, but would aid establishing my ownership if it's subsequently found.