I'm going to have to disagree with some of you on the durability of shell, especially when it comes to scrapes. I have a pair of Alden shell LHS that I scratched on a barstool. No matter what I do to them, I cannot get the scrapes out. I tried a deer polishing bone, brushing, buffing, etc, but nothing works. I took them to B. Nelson shoes, and Nick told me there really isn't anything that can be done.
I also spilled a little kitchen grease on them, but didn't notice until several hours later. The grease left behind dark spots on the shoe. I tried buffing, brushing, etc. on those spots too. Nick also gave it a shot, but nothing worked.
If I had done either of the above on a pair of calf shoes, chances are, I could have gotten the stains out and/or polished over the stains and scrapes to the point where they would be unnoticeable.
Depends on what the scratches look like. If it's a gouge, where the surface of the leather is actually torn, then any material is going to suffer from that. While using my shell boots as real durable boots, they haven't gotten any gouges or surface tears, and that's from plenty of exposure to things that would destroy calf (exposed metal, scuffed on rocks, etc.) My calf shoes though, very often get surface tears on the toe just from the occasional bump, just a light tear to the grain and that's that, permanent.
For just scratches, well, this is going to be a subjective thing. When shell is scratched, the scratch can easily be buffed out 90%, but not 100%. I have tons of scratches on my shell boots, they appear as just lots of fine lines all over the place, especially after I give them a water brushing. For a quick fix, I lick my thumb and rub the scratch hard, usually blends it right into the shoe. The difference is that with calf or CXL, those scratches never get so indistinct, they always show as discolorations (though CXL can be rubbed out to some extent). You can wax over them if you'd like, but they are still scratched.
If you're looking for a leather that will end up looking 100% brand new always, well, you're never going to find that. Shell is much more durable. It isn't invulnerable.