... BTW, which adaptor would you recommend? ...
I've had plenty of good experience with Novoflex adapters on Sony E-mount and Micro-FourThirds mount. Whether they're the best or not, I couldn't say. One of the nice things about the Novoflex adapters is that I can use an accessory mount for the tripod (ASTAT/NEX and ASTAT/MFT) with these adapters that takes the load off the camera's baseplate when using heavy SLR lenses.
I've had no problems at all with the Novoflex NEX/LEM adapter (or NEX/LER, or NEX/NIK), but Leica M-mount lenses shorter than 35-40mm are only occasionally a good match to the Sony A7 sensor; it depends on the particular lens' design. The A7r and A7s sensors respond differently to the lenses so that will influence what you get with these lenses. The same will be true with any good adapter.
The best of the other mount adapters that I've used are the Rayqual adapters, which I usually get from Japan Exposures (
japan exposures | a personal introduction to Japanese photography). They are the least likely to have focus calibration errors (the infinity index is accurate) of the adapters I've had. Most run about two-thirds the price of the equivalent Novoflex adapter.
The Kipon adapters*I've had are next down the line from them.
The ones I've had terrible experience with are made by Metabones : terrible variances between adapters of the same model, and many that just outright do not fit correctly on either the lens or the camera mount, or both. I returned all of these, the third of which I'd exchanged three times. I won't buy another.
G