Shadow is a physically big bike.
Savage is similar size and weight to a 250.
Shadow is a much smoother bike. If you’re going to be on the highway a lot, the shadow is the nicer bike imo.
As a first bike, neither produce too much power, but the shadow weighs considerably more. I personally recommend the shadow as a first bike only if you’ve taken the MSF and are comfortable doing the slow speed stuff on a Rebel. Everything that is hard at low speed is much harder on the shadow.
Savage is, to my understanding (I HAVE NOT ridden one) much lighter and thus much closer in effort to the Rebel.
Belt drive is easier to take care of, and windshields are cheap (as are bag for a cruiser).
Personally, I’d say the Savage because it is easier to ride, easier to maintain, and has lower mileage. But I am a huge fan of the Shadow, it is a good bike imo. So if you feel up to the effort of the heavier bike, you aren’t going wrong with it.