I own both, but like other people have been telling you, asking this question on gaming sites will give you a very specific biased pool of people for your data: The core gamer. Or rather, the core Nintendo fan.
People active and invested enough into gaming, to go to a gaming website, will be much more likely to have owned an obscure system than the average consumer is. Heck, most of the average consumers probably still arent aware that the WiiU existed and was it's own dedicated system and not an add-on for the Wii.
Like Rol said looking at sales data gives you a more accurate picture. The fact that the Switch will outsell the WiiUs lifetime in it's first year, provided Nintendo can ship enough, should tell you all you need to know really.
Right know the Switch is unfortunately severly supply contrained and not even close to satisfying demand, a situation that never even occured like this for the WiiU.