If I had to choose just one, I would go with Wii U.

Why? My gaming tastes. I love Nintendo games.

I can't say I can recommend it for you unless you love Nintendo as much as I do. If you do, then the console is fantastic.

Between my Xbox One and My PS4, I play more PS4 by far. So I guess that would be my recommendation: PS4.

Why?

Great console even if you don't get ps+.

What I like about it when comparing it to my Xbox One: It lets you play your games almost instantly. I often have to wait 10-20 min for it to install depending on the game when I buy one for Xbox. PS4 is faster.

Joining parties is simpler, at least for me. PS4 also turns on faster and has a simpler UI/dashboard in my opinion.

What I love about my Xbox One: The controller- best ever in my opinion. Also, there are a lot of games I like on Xbox, Gears of War, Halo, State of Decay, Alan Wake, Crackdown to name a few. All of those and more are sure to be seen on Xbox One.

I like all three of the consoles. It's a hard choice although some will say it's a no-brainer.

Take a look at the lists of upcoming games on each, go with your gut on what interests you more.

Edit: almost forgot- What I love about my Wii U!: The gamepad, more useful than you might think. The games! I love Nintendo games. Pikmin 3 was awesome, Wonderful 101 was a blast! Bayonetta 2 was spectacular.

Mario Kart 8, Wind Waker HD, Hyrule Warriors, Zombi U, Monster Hunter, Captain Toad, Smash bros. and Mario 3D World are all fantastic games.

There are several great indie games as well. 

PS4: best multiplatform performance of the 3, long term probably the most "must" have titles on it and even though you don't intend to pay for PS+, the offers for PS4 will surely become better the further we get into its life and suddenly paying $60 (or 40quid) for 24games+ online might sound like something you wouldn't mind ;)

So far all PS4 has is Bloodborne and that's definitely not a title for everyone.

I can say this, if you game on your "main" TV, the same one you watch TV, movies, etc, no other choice than Xbox One. The HDMI through and how you're always connected within everything on that screen without ever having the need to switch inputs on your TV is revolutionary when it comes to gaming. You can instantaneously jump from watching television to gaming, to youtube, to twitch, etc.

I read the OP again and I think I could answer better this time. Since you're not going to wait until E3, which would be better, at the moment the Wii U obviously has the best exclusives. The XBO has a better selection of games compared to the PS4 at the moment as well. However, I feel that by the end of the generation the PS4 will have a better and wider selection of games compared to the XBO. The XBO will get big Japanese games like FFXV and KHIII, but I doubt it'll get support from the smaller Japanese devs.

So pretty much if you can't live without the Nintendo staples like Mario and Zelda, get the Wii U. If you can't live without Halo and GOW, get the XBO. If those two conditions don't apply get the PS4, because in my opinion it will have the largest and maybe most diverse library by the end of the generation.

I gave a second answer after reading the OP more carefully.

Exactly how I feel.

IDK man, if you are only buying one this generation, it kinda does depend on your personal gaming tastes.

Honestly, without Zelda coming out this year, and with local multiplayer being off the table, just get a PS4. I'm sure there will be a new Nintendo system by 2016, so I'd just wait and get that if you really want Nintendo with free online.

If you have a gaming PC, most games will be duplicated with a PS4 or an Xbox ONE. In that case, a Wii U would probably be the perfect console for you. And that one at has free online and yes, most games who have multiplayer also have online multiplayer; they're just missing online chat (and 8-player smash). But considering what I generally get to hear on those chats, I prefer linking up my PC with Teamspeak and a gaming group I know for that, so no loss for me at all.

Many of the Playstation 3 and Xbox 360 games you have played are already waiting on the Playstation 4 and Xbox One. There are a few exclusives which you can get for either of those but not as many as you would find on the Wii U. If you haven't owned a Wii, I would recommend this option.