Lens correction

Is it better to allow in-camera correction and then do more correction in Lightroom via lens profile, or use camera only correction, or only correction in post?

See for yourself.

Shoot a good grid pattern. Brick walls are a good subject for this. Make sure the camera is level (a tripod and a level are best).

Shoot several frames at different focal lengths. Shoot some with in-camera lens correction, some without.

Process and compare. Which are best?

Without knowing your camera and lens models, no one can say better than you can say yourself.

Unless I am not up-to-date with the newest models (a real possibility), I believe that in-camera lens correction is done only during jpg processing. So if you are outputting Raws, you have the option to do LR correction or DPP correction, but not both. LR comes bundled with relatively few correction profiles that can be used with rendered RGB images (jpg, tiff, psd) because of the possibility of jpgs receiving double corrections, camera and LR, which could be undesirable.

Since DPP does DLO lens correction to CR2 files, which produces a double Raw containing corrected and uncorrected versions, I suppose the same technology might be in current models (please tell me if it is), but LR/ACR will not open the corrected version.

I had to turn off in camera processing on my EOS-M. It turns out that it WAS making corrections to the RAW files. My normal workflow has all RAW files run through Lightroom, which is also set to correct the images. I was suddenly getting images corrected twice, which obviously introduces unwanted distortions. It seems LR 5.3 cannot tell that a RAW file was already corrected.

If you have a RAW + Lightroom workflow I would recommend turning off in-camera corrections and let LR handle that load.

I mostly shoot RAW + ML with my 60D's so prefer a consistent workflow, and since some of my core lenses are *not* Canon and not in the database, I don't want to keep track of what is corrected in-camera and what is not. Much easier to let LR handle the load.

If you don't do much PP and don't use LR then try leaving corrections on in the camera.