I'm probably going to get bashed for this, but I honestly don't feel Mario games change very much between titles. To me (as in, in my own opinion) they just feel like the same game over and over and over. Some games break this chain, like the sports/racing spin-offs and Super Mario Galaxy. And I actually enjoyed Luigi's Mansion, Yoshi's Island, and stuff like that. But New Super Mario Bros Wii? Why remake a remake...? Yeah, the four-player, I get it, but... Why?
Technically, LoZ is pretty similar, it's just less popular and has less spin-offs. But they're still different enough (personally) for me to enjoy. The NES days were different though. Back then, Mario>Zelda, definitely. But times change. Zelda's made itself more awesome, and Mario... Is just Mario. Popular, but not the best. I just vote based on gameplay rather than how iconic the main character is. And while Mario is definitely more iconic and well-known than Link, I just like the LoZ series more than the SMB series.
Really though, I don't usually get a game when it first comes out, for money reasons. And by time I can afford it, I'd have seen enough gameplay and such that I could decide if I really want it. I go by game rather than series. Give me a specific game from SMB and a specific game from LoZ and my opinion would most likely be different.
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When life gives you lemons, screw the world and grab a soda.