Both have things going against them. GT6 was released around the same time as the PS4 and Xbox One came out. The release being after the PS3 has been on the market for 7+ years, so many people were ready to move on. Mario, on the other hand, is launching on a console that has only sold 5M in 1+ years. Unfortunately for Nintendo, it doesn't look like even Mario is enough to completely overcome the disinterest in the Wii U HW. In the end, they will both do decent numbers. Just not as well as the previous games in the series.

If it had been a main series Mario title, and not a side-series game, I think there would be MUCH more interest in the game. From what I gather about Mario 3D World, it looks to be a rushed game that may have originally been a 3DS project.

Install base is a HUGE factor. 1.55 on a 80 million install base isn't as good as 1.31 on an install base of 5 million.
GT6 attach rate: 1.9%
SM3DW attach rate: 26%

you spin me right round baby right round like a record baby right right round round. 

Mario 3D World is a main series title.  It's not like it's Paper Mario or Mario Party.  If you mean '2D' Mario, I doubt it.  The Wii U already had a '2D' Mario, and that didn't change anything.  People just aren't as interested in the HW, not like they were with Wii.  The only thing that I really think that could possibly turn that around is a drastic price cut.  Something I don't think Nintendo is willing to do, as they'll be losing too much money.

LOL it's funny watching people try to make excuses for GT6's sales or logically explain them away. I mean some in this thread are actually making it out to be that releasing the game after/so close to PS4 is a negative thing. How many posts did we have to read all year about how gamers think it's great that Sony was releasing big games like GT6 in 2013 with PS4 launching and yet now those same people are saying gamers don't really care about the game because you know, next gen is here. It's funny.

If it were really that simple I highly doubt Sony would have bothered releasing the game. It's just a disappointment, it happens. Sometimes you release something to market and people just don't want it as much as before. You guys should hope it's just franchise fatigue and that a good PS4 debut will return the franchise to its former glory.

By the end of January.

Actually this time it wasnt a Nintendo defender that brought Vita up. Someone said Wii U was in a sales war with Vita, implying that Wii U is selling horribly

Nobody is sugar coating anything, look at the actual conversation. DSP333 said 3D World was supposed to cause Wii U to sell better than Vita but didnt. Bosslug pointed out that ever since 3D World came out Wii U has been outselling Vita. Nobody claimed thats a great accomplishment, only correcting a false statement from a poster.

for future reference It helps when u actually read the quote tree ur replying to

Double standards are to be expected when nearly everyone is biased.