Yeah go with Mario Kart. There's not that many games in the series so it'll be a nice break after Zelda since a Mario Kart poll wont take long.
If I did Mario... whew. Would Luigi's Mansion count? Wario Land 2/3/4? Super Mario Land 3/Wario Land 1? Yoshi's Island? Yoshi's Story? Does Super Mario Bros DX. for the GBC count as enough of a separate release? Could be interesting.
If you do a Mario Platformer poll, only do the Mario platformers were you actually play as Mario. Even though Yoshi's Island and Wario Land 1 both have the Mario name in the title, both games are really the start of Yoshi and Wario's own separate series. The only reason both games contain the Super Mario name in the title was so it could help both series get off the ground. This is why the sequel to both games, Yoshi's Story and Wario Land VB no longer have Mario in the title.
Luigi's Mansion isn't a platformer so it shouldn't be counted at all.
On the issue of Super Mario Bros DX, I'd say don't count it for the same reason I would also say not to count Mario-All Stars and the Mario Advance releases. It'll just create a giant mess and split a lot of the results. If say SMB3 got the most people voting for it in a certain round, but all the votes got split between the Original, All-Star and Advance versions of it and as a result something like Land 1 ends up winning over it because all it's votes went to it's only version, that wouldn't make a very good poll now would it.
I'd say for a Mario Platformer poll, just include Super Mario Bros 1-3 (count both American and Japanese version of SMB2), World, Land 1-2, NSMB DS and Wii, 64, Sunshine, and finally Galaxy 1-2. This way it'll be simple and to the point and we won't have to get into arguments about different version of certain games messing up the results.