I've had a Marlin 1894c for several years; it was my first centerfire rifle and is still probably my favorite to shoot. It's so handy and fun and has such great practical accuracy--within the limitations of its range. I've done a good deal of loading and chronographing with it. My favorite loads in .357 are a 158 gr Hornady XTPFP over a max book load of Little Gun for 2,000 fps; or a 125 gr HP over a max load of H110/W296 for 2,150 fps. Both are very consistent and accurate. I've used heavier and lighter bullets, and cast bullets and swaged bullets, but settled on these standards as able to do anything that's reasonably within the capabilities of the .357 in a carbine. .38's are fun for plinking, and I've shot plenty of 158 gr. RNFP and LSWC through it for fun and in cowboy action games. Oh, and a final plus for the Marlin: it's super easy to reload for.
I was issued an AR last year by the Sheriff's Office. To me, it's not as fun a gun to shoot as the Marlin. Nevertheless, there is NO DOUBT in my mind that it's the one I would prefer to have in a fight. The handling characteristics, capacity, longer range capabilities and fast reloads make it all business for me. I shot the Marlin in several 3-gun competitions several years back and became keenly aware of its limitations, and the AR overcomes all these; but it's still not as fun to handle and shoot, for me.
In terms of terminal ballistics I don't have any practical experience to share; just the opinion that I think either one would give you a pretty good margin of potency within 50-75 yards. Past that, the .357 starts to give up ground pretty fast.
