Of digital SLR bodies I've had and used, I've had the D30, 10D, Digital Rebel, Digital Rebel XT, Digital Rebel XTi, 20D, 30D, 40D, 1D MK II, 1D MK III, 5D, 5D MK II, and the 7D over the past 10 years. Usually at least two at the same time. Most of them I bought used and sold them after a year for more than I paid, but my 5D MK II will be three years old in about three weeks. I also had a Kodak DCS 620, but it was mostly as a collectible, and not used other than to test.
In order of IQ, I'd say 5D MK II, 1D MK III, 7D, 1D MK II was what I saw. Certainly the 1 series cameras have a lot more going for them besides IQ, the ability to AF at F/8 or even f/11 (with stacked TC's) is a huge plus, and will be missed with the 1Dx, if I decide to get one.