2DS-Have one, still play it. Currently playing Pokemon Sun and a few other games.

WIIU-Don't have one and not planning on getting one.

Switch-Don't have it, but I am planning to get it for Zelda and the new SMT coming for it.

3DS XL - Fire Emblem Awakening LE model; still playing Chrono Trigger DS, Ocarina of Time, Fire Emblem, Dragon Quests and others from time to time.

Wii U - deluxe version; rarely played.

Switch - grey version; I currently own BoTW (I finally got a copy today) and I am Setsuna (not recommended at full price); future buys will most probably include Lego City Undercover, MK8 Deluxe, SM Odyssey, Xenoblade 2, Fire Emblem 2018, DQ XI and quite a few indie games.

2DS - gave my kid one last year. He plays Yokai watch and Pokemon, although not very often.

WiiU - still use it for Wii Fit since launch. My kids play lego games on it and use it for you tube.

Switch - Zelda!!!! We tried 1-2 Switch and Snipperclips briefly, yet Zelda steals all our time.

3ds x 14 approx (includes 2ds limited editions). Don't have time to play

Wii U x 1 only playing Zelda

Switch x 0 will buy when bugs ironed out

3DS: I have a New 3DS XL and it's my main gaming platform. Recently bought Dragon Quest VIII and Story of Seasons: Trio of Towns, plan to buy FE: Echoes, Culdcept Revolt and RPG Maker FES. Still hoping for new games announcements and localization of others, like Monster Hunter Stories, Lady Layton and Dragon Quest XI. 

WIIU: I have the Deluxe model and still play it, Zelda: BotW is the last game I bought for the system.

Switch: Don't own and don't have plans to buy one anytime soon, I've disliked the concept since its reveal, so the games it can get will be the deciding factor. It'll need good exclusives, a ton of them, for me to buy one. 

3DS
Yes, one XL version. (No NewXL)
Rarely play but most for OoT and MM 3D.

Wii U
Yes. One Premium Black since launch.
Right now I use for Splatoon.

Switch
Yes. Neon version.
Play everyday with BotW.

Edit:

Interested in these games for Switch:

Splatoon2, XC 2, SMOdyssey, FE 2018, Skyrim.

3DS, yes, 1 (original)

WiiU, no

Switch, yes

I own a 3DS XL, I'm still using it for Gunvolt 2

I own a Wii U and lately I don't use it anymore, sometimes to play Splatoon

I don't own a Switch yet but I'll buy it on summer (along with Mario Kart 8, Splatoon and Super Bomberman R)

3DS: Own the Year of Luigi XL one and the Majoras Mask New 3DS, have quite a few games for it and last played Pokemon Sun

Wii U: Own it, have most of the big first person releases on it

Switch: Own it, currently have Zelda, 1-2 Switch, and Bomberman (physical) along with Snipperclips, I am Setsuna and RMX (I wish there were some physical releases for these!)

In the near future I'm rather excited for the new Shovel Knight, Blaster Master Zero (talk about an overdue sequel), Metal Slug 3 (those neo geo titles are impossibly expensive to own the original copies of), Splatoon 2, Mario Kart Deluxe, and eventually the new Mario game. I'm sure there's plenty I'm overlooking, but that's enough for now.

2 3DS standard and XL, use occasionally especially long trips

wii u gets fairly regularly use

Switch plan to get one sometime in the next 2 years but not overly keen on the first gen version. I think November will be the earliest I get one unless some super deal comes my way.