For Mario, I recommend Battlefield or Pokemon Stadium 2. These stages are typically better for Mario, as the platforms enhance Mario's up-air strings. Mario's up-air strings is Mario's most important feature, without Mario will probably be low tier. Against Ridley, a somewhat heavy character with a big hurtbox, juggling is key to racking up damage for a potential kill. but there are some faults too. Battlefield's bottom blast-zones are really low, so if you hit a f-air spike, Ridley could live, with his good recovery and all. Pokemon Stadium 2 has closer bottom blast-zones, so if you spike Ridley there, there's a less chance he'll live. But, Battlefield's platform cover the entire stage, making it possible to hide under them and start a string. With those platforms, you could start you up-air at ground level, then slowly jump on the platforms during the string to extend it. If you finish with and up-b at the top platform, it might even kill. Pokemon Stadium 2's platforms, are somewhat separated. Sure, you could extend your string with one of the platforms, and finish with an up-b. But there is a lesser likely-hood of that killing then the battlefield version. So honestly, it's your choice.
Mario