Since BF and Christmas is coming soon I wanna ask which one is better to purchase. Originally I want to buy NSMB2 but with the current My Nintendo Reward Xenoblade is now below $35 so I don't have to purchase $50 card anymore. I know it's a different genre but I would like to know which one is worth buying. And before u ask I'm already finishing both Xenoblade (although without doing sidequest and with a bit cheating) and NSMB on Wii and on original DS. 

And this is my first BF with I'm going full digital on Nintendo. Does Nintendo usually give some discount?

Xenoblade

NSMB2 is worst of the four NSMB games, so I think you should go with Xenoblade 3D.

And how about post game content? IMO Mario wins because replayability. But I've never play NG+ on Xenoblade so I don't think that's fair. Any Opinion?

Xenoblade

NSMB2 is the worst in the super mario bros series. It is barely a 7.5 or even an 8, and i played it for 15-20 hours max.
Meanwhile, Xenoblade is one of the best JRPGs in history and probably the best one of last generation. The main story should take u atleast 50 hours, even more with side content and NG+. I think you should definitely go for Xenoblade.

Xenoblade for sure

Wew I thought ppl will suggest Mario since its more popular. Seems like NSMB2 is really crap lol. Now I just gonna wait for my new SD card to arrive since I only have like 5000 block more on my current SD card.

Xenoblade, no contest.

ive not played xenoblade before but i can tell you NSMB2 is just the same as any other NSMB game. None of them are very good they are all way too samey. Feels like the same game we been playing since the 80s. Go for Xeno is its very highly regarded