The 3DS was a terrible console in my opinion, I never really liked it. Games on it were underwhelming, the hardware was disappointing and I really did not enjoy the design of it. So, the Switch is so much better than the 3DS.
I still have a soft spot in my heart for the Wii U, I really liked the idea and a lot of the uses out of gamepad. i personally really like it as controller. But overall the Switch is so much better technology wise, portability wise, game wise, and many other ways.
Check out my lastest games review: Fast RMX and Snipperclips: Cut it out Together