Wii U for it's first party titles, Miiverse, and Gamepad. (although, I do love my 3DS as well)
I have an Xbox One, and I love the games I'm playing on it. But as a console, I hate the system menu, I hate having to install the games before I can play them, I hate that I'm going to have to un-install games once the handful that I have fills up the system memory (I'm over 80% memory used and have only had the system for 5 months) and then have to re-install them if I ever want to play them again after deleting something else.
So yeah, as a console, the Wii U is my favorite of this gen.

At the moment:
-My Vita has been dead for at least a month. Probably a couple of months.
-3DS gets regular use thanks to Xenoblade and a few smaller games.
-Xbox One gets used daily. Mostly for media features and RER2( which is a available on last gen hardware)
-PS4 is gathering much dust until Batman arrives. Can't remember using it.
-Wii U gets fair amount of use but nothing special. Had the best library for my money but need a steady flow of new games. Not hyped at all for Splatoon, tbh.

I guess the most used overall is 3DS.
Most used home console is the Wii U.
If I could only keep one, it would be the Xbox One (best mix of first and this party support power and features for my personal taste)

Gonna vote XB1 this time.

For the record, 7th gen hardware still rules in my home (own all of them, too!).

It's a handheld console.

1. PlayStation Vita - Amazing handheld I have played almost every day since i got it 18 months ago. I love the games, the system and controls. A near perfect system for my tastes. 9/10

2. Nintendo 3DS - A great system that only fell into 2nd place recently. Gives me everything I want from a Nintendo system with great Mario and Zelda and titles like Fire Emblem. 9/10

3. PlayStation 4 - Only now has the PS4 come into its own, but it is doing great and shaping up as a possible monster of a system. Everything Sony did I like from the controller, the rest mode and the UI. Great system with amazing potential. 7/10

4. Nintendo Wii U - Similar to the N64 this is a great Nintendo system, unfortunately little to third parties mean the library is thin. Still worth your time, especially after Xenoblade came out. 6/10

5. Microsoft Xbox One - With Japan completely ignoring this system the library has a total of one game (Sunset Overdrive) that I could see me wanting now or for the next year that I could not get on my PS4. Not a bad system, but feels a bit redundant for my tastes. 3/10

Came to the thread with Wii U on my mind as the response, but once seeing 3DS, it was the obvious answer. Sorry, but even if games like SSB or SMB3DW are better than their 3DS counterparts, the amount of games worth owning on the 3DS exceeds the others.

3DS for consoles and portables. Wii U for console only. Bloodborne is amazing but when everything else outside of a few ports are rather meh, then the PS4 can't contend.

In a year or two from now it's possible my answer will be 3DS and PS4.  PS4 should pass the Wii after a handful of quality games come out, but two years from now, highly unlikely the PS4 surpasses the amount of quality the 3DS has even if no more 3DS games were to release. 

I only own a Wii U, and I already know that I'll have more fun with it than with the 3DS and PS4 that I'll eventually get.

3DS offers Monster Hunter 4 Ultimate, which is pretty much the only reason I want the system, but it also has many appealing games, both at retail and the eShop

I decided to go for PS4 since Star Ocean 5 will be exclusive to Sony, add Final Fantasy XV, Persona 5, and the almost guaranteed exclusive JRPGS that they system will have over Xbox's Scalebound, and I'm sold. Hopefully Twisted Metal and Gran Turismo will see new entries as well.

Wii U for the win!

For now I'll say the 3DS. This generation for me at least has had a fairly slow start, not too many console games that I really want at the moment so my use has been limited. My Vita library is also really small so that only leaves the 3DS.

I've enjoyed my time with the 3DS though, quite a few games I've been enjoying on there and still a fair number of titles I want to pick up.