The text below is by amfoto1. I took the quote tags away, to easier add my comments in red inside the text.
It's not a ranking, but a general summary of the various models AF systems can be found here
. This just lists the number of AF points, whether or not they have Live View/Contrast detection focus, and the number of dual axis or "Cross type" points and a few other differences.
There are so many different factors and features that effect focusing and how cameras might be ranked... Plus it would depend upon the planned use of the camera. Lenses used with the camera make a big difference, as well.
As briefly as possible, starting with the APS-H and full frame models....
1D series cameras use essentially the same 45 point AF system as the film 1V and EOS-3, with 19 dual axis points. Over time this system improved and features were added. I believe the the 1D Mk IV was the first to have Live View and also saw increase to 39 dual axis points. Earlier 1D series cameras had only 7 cross type points in the center. Worth noticing is that most of these cameras don't have any cross type points at all at f/5.6, one in the center at f/4, with the rest of the cross type points coming alive only with f/2.8 or better. A 7D has 19 cross-type points allready at f/5.6.
1Ds series all use basically the same 45 point AF system as 1V and EOS-3, 19 of which are dual axis. AFAIK, none has Live View. The 1D Mark III was the first with live view, and the 1Ds Mark III was introduced later.
Center point on all the 45 point systems used in 1D/1Ds models is f8 capable. 1D/1Ds series enjoy some other features, including specialized groupings of AF points and spot metering linked to the active AF point.
5D and 5D Mk II use a 9 point AF with only the center one dual axis, but in AI Servo mode there are 6 hidden expansion points available, clustered close around the center point. Two of those expansion points are dual axis type. 5D classic does not have Live View, 5D Mk II does. Center point on both the 5D and 5DII is f5.6 capable.
1DX and 5D Mk III both use 61 point AF system, with up to 41 points dual axis type (varies a bit depending upon lens). Both have Live View and both have five center points that are f8 capable. 1DX is more configurable than 5DIII. This AF system is unusually low light capable, able to focus to about -3EV (moonlight, or about 2EV lower light than most other Canon systems). These cameras also have five high-precision cross type points, thus being the first with more than one such point.
6D has a unique 11 point AF system with a single dual axis point at the center. The center point only is rated to -3EV light. The others are -1EV approx.
Among the APS-C cameras...
D30 and D60 both had 3 point AF systems that are essentially a carryover from earlier film Rebel/Kiss models.
10D and Digital Rebel/300D got an upgrade to a 7 point AF system that is essentially a carryover from the earlier EOS-30/33/Elan 7 film cameras. I seem to recall the center point is dual axis type, but am not certain. Essentially this same system was also used in the Rebel XT/350D and XS/1000D.
20D and 30D got an improved 9-point AF system, with center point dual axis type. Essentially the same was also used in the Rebel XSi/400D and XTi/450D, T1i/500D, T3/1100D, T2i/550D, T3i/600D and SL1/100D.
40D, 50D and 60D saw an upgrade to a 9 point system with all 9 dual axis type. Live View was also offered on these models. This system also is used in T4i/650D and T5i/700D. 40D was the first APS-C model to get the AF On button on the back, right after it was introduced on the 1D Mark III. The 40D was the first EOS camera ever to have a high-precision cross-type point at the center.
7D introduced a 19-point, all dual axis type. It is sort of a scaled down version of the earlier 45 point system in the 1D/1Ds/1V/EOS-3, but only using the cross type points that system featured. Except that it's also got some configurable aspects, similar to 1D Mark IV. The 7D introduces Canon's first active matrix/transmissive LCD focus screen (later also used in 5DIII, 1DX and 70D). I'd rather say this is precisely the 9-point system from the 40D upscaled to 19 points, since the extra ten points fit in between the nine points in the 40D. The 45 point systems are quite a bit different, though.
70D's AF system is very similar to 7D, except slightly scaled back to offer only custom three configurations, compared to the five offered by 7D.
All the APS-C cameras are limited to f5.6 capable.
1D/1Ds series and 7D use a discrete chip to drive AF. Most other Canon share this duty with the other functions of the main processor, which is also handling images. Don't know if this is the case with the 70D, 6D or 5DIII. According to the information available from Canon, the architecture often has one chip doing image processing and another doing the rest in the camera, AF included. In some cases the imaging processor augments AF calculations. Top (fast) models have a dedicated AF processor, and may have dual image processors. The 1DX is the only one also having a dedicated AE processor.
1D/1Ds Mark III were the first to get Micro Adjustment feature. The 5DII and 50D were the first non-1D series to get it. It wasn't carried over into the 60D, but is a feature on the 7D. An improved, second generation version of MFA is in 5DIII, 6D, 1DX and 70D. It increases from 20 to 40 lens configurable. Also it is lens specific (by serial number), where the earlier version was only lens model specific (so if you adjusted one EF 50/1.4 lens, the same would be applied to all EF 50/1.4 used on that camera). Also, the latest version has dual adjustments for zooms, where the earlier version only offered one.
The T4i and T5i were the first to offer AF during video, limited largely to STM lenses I believe (I don't shoot video with my DSLRs, so someone correct me if I'm wrong). The 70D is the best at this now, with it's newly developed sensor based dual-pixel AF in Live View and video.
Was it the T4i or T5i that was the first with a touch screen? Heck, I'm confusing myself now! 
Those are the major points that come to mind.
