The way I see it, the people who will be looking to buy SSB4 fall under one of four different scenarios which are as follows:

#1. People Who Own A 3DS
#2. People Who Own A Wii U
#3. People Who Own Both Systems
#4. People Who Don't Own Either System

Right off the bat it's pretty obvious that the 3DS version has a tremendous advantage in Group #1 and Group #4, both of which are the groups that matter most since they have the most people in them by far. I mean to get SSB4 3DS, we're talking $170 lowest entry point (or $40 if you have a 3DS already) v.s. $360 for SSB4 WiiU, disregarding future price cuts of course. It's pretty clear what version the majority of people in these groups are gonna go with. Now Group #3 holds a more even battle, as the people there have both systems so there's only a $20 advantage for 3DS version. However, as of now, there's nothing fundamentally better about SSB4 WiiU that offsets that $20. Yes it looks better, but I doubt the majority are gonna pay extra just for a better looking game. Plus with the 3DS version selling more to begin with thanks to Groups #1 & #4, their friends are more likely to have the 3DS version, encouraging dual console owners to follow suit. Lastly, Group #2 is pretty much the only one where the Wii U version has a clear advantage, since a Wii U only owner would only have to pay $60 for SSB4 as opposed to $170 for 3DS + SSB4, so of course the majority of this group will get the Wii U version. Wont be enough to outweigh the other three groups though, not by a long shot.

combined it will def pull off the highest in the series and top all other paid fighters. WiiU should at least do Melee numbers and 3DS is a potential 10m seller, 7.5 min.

To be honest how much it sells will depend on the platform content and the connectivity and the differences between both games. I have a feeling they're playing some stuff close to the belt in regards to that

Seriously i think it can reach 15 million, definetly it will reach 5 millions on both plattforms, i dont think 3ds and wii u sales really hurt each other. Its the other way around if you like it on wii u you might also play it on the go and if you ike it on the handheld you might want to play it in big.

Well i could be wrong though i never studied those things, thats just my expectation

Uhm. That's literally everyone.

Yes, on the question whether or not it'll be the biggest fighting game this generation. Probably even just the WiiU version separate.

I think the WiiU version will easily come out on top, simply because the console experience will beat the handheld experience. That said, the 3DS version should do very well, because it's the first handheld entry in an extremely popular franchise and looks amazing. I don't see the WiiU version beating the Wii version, because of the WiiU's lower install-base and the fact that the each version will slightly cannibalize the other.

I'd say;
WiiU: 7.5m
3DS: 4.5m
for a 12m total.

So, in other words, the 3DS will be a watered-down port?

It's coming on the 3DS and the Wii U. I am sure this is going to sell more than brawl! I say 13 million+ lifetime!