After much research, I bought the Commlite adapter, but other users' input regarding others would be appreciated.
The current EF to FE adapter situation is very mirky. I would like an adapter with better AF speed than ones on the market right now, even Metabones III, now IV. Also, even the better-reviewed ones like Metabones and RJ adapters are supposed to not work well with third-party lenses especially Sigma, which is disappointing since the advent of Sigma ART 35 and upcoming ART 50mm lens. My research so far turned up the following.
The ones without AF are pretty cheap, but there are quite a few that preserve AF, IS. From researching these in an effort to find a reliable one, the user experience seems to be that AF is similarly slow via all of them, and each has different electronics/software leading to one working better with some lenses while another adapter may work better with other lenses (Canon or third party).
Metabones Mk III adapter seemed to be the most popular with most user reviews but also the most expensive at $400.
Metabones Mk III's AF speed is slow and typical:
It's since been updated with Metabones Mk IV, but disappointingly, according to Metabones, there has been no AF speed improvement from Mk III to IV, just bigger opening to accomidate tilt-shift lenses and anti-reflective coating inside:
This Youtube video comparing Viltrox, Metabones IV, and Commlite also seems to indicate Commlite may work even better than Metabones IV:
Mk III did not work with all lenses, only Canon-branded lenses introduced in or after 2006 are officially supported. Autofocus may be disabled for older Canon lenses and most third-party lenses, including most Sigma, Tamron and Tokina lenses and all Contax N lenses. A lot of users are reporting internal reflections causing funny colors and CA at edges, and there is a DIY fix using adhesive-backed velour to cover up the adapter internals.
However, Metabones IV is reported to be too tight on lens side fit along with other issues. The video also shows why non-smart adapters like Vello can't be used:
My next choice would be RJ Electronics one which is cheaper with good user reviews available. Some claim it gives sharper results than Metabones III (how?) and works with older Canon lenses unlike Metabones. RJ admits it does not work well with Sigma lenses. I read one user who said that Canon 100L Macro did NOT AF when focus limiter was set to 0.3-0.5m (Macro range) but AF was fine at other settings.
This Viltrox zinc-alloy one seems okay as well. I have a Viltrox Canon EF to M adapter which works OK though a bit loose on camera end. One can find a couple of user reviews on line, so at least you know it "works."
I found a video on Youtube that shows AF speed with Viltrox adapter:
Fotodiox Pro adapter, at similar price to Commlite. The lens side is metal, but camera side seems plastic.
AF speed seems similar to others.
TechArt version II adapter.
It's thought TechArt and RJ adapters may be from same oem, sharing the black finish on the camera side and also sharing the inability to recognize focus-limiter on Canon lenses. It's selling a little cheaper than RJ.
Deo-Tech Falcon adapter
This one also looks to be the same adapter as RJ and TechArt
Upon further research, some users including Fred Miranda are reporting that RJ/TechArt/Deo-Tech adapters are softer with more CA in the edges compared to Metabones III.
Deo-Tech now makes Mk III, which now shows the label "Tech-Art"!
Well, I ended up returning the Sony A7r but recently bought it again with the Zeiss FE55 f/1.8 lens. The adapter I did end up getting is the Commlite FE-NEX adapter. Based on reviews I read, none of the adapters, even the pricy Metabones, auto-focuses fast, so I bought one that is reported to have AF at least as good as others with least reports of issues.
This Youtube video comparing Viltrox, Metabones IV, and Commlite also seems to indicate Commlite works even better than Metabones IV:
Commlite FE-NEX adapter:
Good news first. Its build quality is quite good with nice metal contact areas and sturdy-feeling switch and smooth mount/unmount. AF speed was surprisingly fast with Canon lenses I most likely would want speedy AF from, e.g. Canon EF 24-70 f/2.8 II, Canon 35L.
BTW, It's a joy to use the Canon T-SE 24mm II with its fabulous MF ring with this adapter and Sony's focus peaking. Fantastic!
Now bad news. Longer focal length lenses don't AF as well with lots of hunting issues. Canon 100L macro was especially slow with no useful AF to speak of. I expected better, but Canon 70-200 f/2.8 II did not AF well at all with the adapter setup. Pity that... To add to the insult, Canon 85L II would not even mount physically on the Commlite adapter. Something catches mechanically and the 85L cannot be screwed on all the way.
All in all, I got pretty much what I expected going in, with nice build quality for the low price I paid.