Go with the RF Mount version. You won't get all of the features of the camera with the EF version. Such as 12 fps or support for Dual Pixel Autofocus. If you're using the Gen 1 copy of the lens.
Great point Demetrius.
You also won't get the native Control Ring options unless your adapter has that. In truth there is little or no reason for you to consider anything in an EF mount. RF makes more sense from an investment stadpoint as well. Lenses with shorter FL's remain affordable. The RF 100-500 is a great super telephoto for the R7 and not exorbitant price wise.
I think we are going to see a shift in lens offerings. Zooms are now becoming more capable of rivaling the optical quality of primes. These are affordable. The exceptions are the new gen of super zoom (example 100-300), as many don't have $10k + to blow on one lens. Right now is a great time to pick up a lens or two for your camera. Both Canon and B&H are having a tremendous sale on RF lenses. Canon has some great refurb options and B&H has brand new L series lenses deeply discounted. You may not see these prices for the sales coming on Independence Day.
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12/05/2023: New firmware updates are available.
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.