I have 2 rotties and 1 gsd now my rotties are goofier, as far as smarter and more loyal that's a toss up, longest life span I had a gsd as a kid that passed at age 14 the oldest rottied I had was 12 first rottie was 6 and my 3rd rottie was 8 when they were pts due to bone cancer I would get both again
Racer has direct experience. I'm only quoting anecdotal information:
1. Typically larger dogs do not live as long as medium dogs.
2. Rotties have lots of documented health problems, but if you get pups from a professional breeder, you can get documentation screening out the common problems.
3. I think that Rotties are friendlier with people. Both GSDs and Rotts have to be socialized with lots of people, but for different reasons.
4. A socialized Rott is gentler and less pushy, a socialized GSD is less reactive and friendlier.
5. I think a GSD is more intelligent and easier to train. I guess you might call a GSD more loyal.
6. I have a Lab-GSD mix - excellent dog. I had a GSD-Dobie mix - lived for 17 years.