While I don't have the AT cartridge (but have other AT models), I do have the Ortofon VMS20E MkII. In terms of specs, they both have a nude elliptical stylus but I think the AT stylus is a little finer and also has a tapered cantilever (which is a positive). I suspect the AT may not be as high-compliance as the Ortofon, which would make the AT a better option if you're putting it on a medium-mass arm.
In terms of sounds quality, I find the VMS20E nice in being relatively mellow and easy listening, but not terribly exciting. I suspect the AT will offer more detail, as they are usually good on detail, and the VMS20E isn't as explicit with detail as some.
If these are both well-used cartridges, you may want to think about the possible stylus replacements. I dare say aftermarket styli are available for both, but they won't be of the standard of the originals. The VMS20E body will take other Ortofon VMS, F and FF styli that are fitted with the universal plastic insert (combination of hour-glass and H profiles) on the back of the stylus. Ortofon still sell an FF15XE MkII stylus which may be suitable, especially if the arm is medium-mass rather than low-mass.