You are absolutely correct. I was actually trying to ask about differences in image quality. I could have written my question better.
The L lens is chosen for "rendering". The Macro is chosen, potentially, for lack of distortion. Which of these two considerations is more important in portraiture?
Hi, I would say that of your two considerations neither is very important.
To me just about any competent lens is probably fine with respect to color quality, provided you set up "properly" for your jpegs (which is your intended purpose). Ignoring the issues of weight, susceptibility to flare, and handling issues, I would say there are two important things in the lens choice. First is the maximum size, as viewed from the front, of the lens aperture. A larger aperture can, in the right circumstances, let you put backgrounds out of focus. The second thing relates to the sense of "realism" in a portrait. It seems mostly a waste of time to talk about it on this forum, but IF you match the angle of view of the final image to that of the image capture there CAN be a striking sense of almost "being there" in an image. This match can be made via the focal length of the lens and shooting distance vs the final "print size" and viewing distance. (I sorta expect contrary opinions here; I would just ask those responders, "have you actually tried it?")
My suggestions for best color in your jpegs are as follows. 1) go through your camera menus for jpegs; set everything to baseline colors, using a "natural" (or whatever term Canon uses) color rendition. Leave things like color saturation and contrast centered on the scale. 2) Put the camera in "manual exposure" mode as well as "manual white balance." 3) Specifically set both exposure and white balance for each specific shooting setup like so: obtain a "white card" that does NOT contain so-called "brighteners" (which fluoresce under UV light, giving a slight bluish tinge). (The white side of a Kodak grey card is fine, OR from an art supply store some "museum grade" "bleached" mounting board. Museum grade won't contain brighteners, but tends to have a slight yellow tinge if not bleached.)
To set exposure pick out a specific scene/setup for your portraits. (I know you wanna move around and shoot freely, etc., but I'm telling you how to get the best color in a portrait.) Put the white card in the scene near where the subjects face will be, facing the camera (note: for this to work it must be frontal lighting, etc.). Mostly fill your camera frame with the white card, and start with some exposure test shots. View the camera histogram (see the camera manual for instructions) after each test shot, with the goal of your histogram spike being close to the right hand side, but not all the way. At some point set the camera's "manual white-balance." (See the camera manual, but as l recall your Canon camera will use an existing test image and will white balance to that. After you set the manual white-balance, test for success by shooting the white card again and look at the color histogram - the red, green and blue spikes should all overlap.) To fine tune your exposure you want white-card pixel values roughly around 235 to 245 (the histogram runs from 0 on left side to 255, so just make an estimate of where to be). Now you should be set up for decent jpeg color and exposure IN THAT SPECIFIC SHOOTING CONDITION. Shoot away all you want in that setup.
A couple comments and cautions: I said you should have both "contrast" and "color saturation" set in the center of the scale. This is not really ideal for that camera. After some baseline test shots with a human subject you will probably want to to set "contrast" and/or perhaps "saturation" up one or two clicks from the center. Do your own tests to decide what you prefer. Second, for darker complexions you will want to increase exposure slightly (moving the histogram spike closer to the right). Note that these camera settings (on your Canon) will be close, but not quite ideal. If you want a little more improvement you will need to use a photo editing program (such as Photoshop, etc.). You would probably want to get to the "Curves" menu, then put a slight s-curve into the line. This will slightly increase mid-tone contrast while slightly flattening both the light and dark ends. (The Canon camera menus don't really allow this sort of tweak.) If you do these things (properly) your portrait tone/color will likely be better than the majority of "skilled" photographers working from RAW files.
Finally, the CAUTION. Don't leave your camera with these specific settings on because they will screw up any casual shooting after the fact. (If you should encounter a flying saucer landing you won't be able to get good photos.) So, reset your camera to auto-exposure and automatic white-balance afterwards.
FWIW if you follow these instructions and the skin tone/color does NOT look good there may be an issue with your monitor set up. For professional work monitors are ideally set up with a custom ICC profile, using special profiling software combined with a hardware "puck" on the monitor. Or whatever modern monitor systems may use to the same effect. OR, it's possible that you used a poor quality light source for the portrait. It should be a full-spectrum light source. Oh, one last comment - this setup method is gonna give a daytime lighting effect; if you are trying for an oranges sunset effect this setup won't give it.
FWIW I have some pretty substantial experience in all these areas; it doesn't come from just reading or watching YouTube videos, etc. I'm glad to elaborate on anything.
Update... Ps, in the situation where you are putting the background way out of focus there could be significant differences in the "character" of the blur, depending on the specific lens. (Bright spots will tend to take the shape of the lens aperture, if stopped down slightly, for example.) So people with specific lens preferences may be looking at such "character." I have very little experience in that regard. But... I might point out that if you are doing group shots, say full length of 6 or 8 people, or more, it will be very difficult to put backgrounds out of focus to any significant degree.