Twenty years of sales for Nintendo consoles and handheld systems has been released in a helpful infographic. While the graph does not cover NES sales, as it's just looking at the past 20 years, and doesn't distinguish between different versions of the same system, it details the sales of every other system.
Based on the graph, one can see that the seventh generation of consoles provided the best sellers for Nintendo. The original DS and the Wii led the pack with 154 million and 101.6 million units sold respectively. This isn't too surprising as this is around the time Nintendo started a serious shift, attempting to appealing to all types of consumers including those who wouldn't typically call themselves gamers.
Sales were not so perfect in the generation afterwards. While the 3DS did quite well for itself, with 75.9 million units sold, the Wii U struggled to match those numbers. According to the infographic from Visual Capitalist, the Wii U saw a total sales figure of 13.6 million units. Those sales numbers make it the worst performing system represented on the infographic.
The Wii U's marketing did not meaningfully differentiate it from its predecessor which meant it was not made to clear to non-gamers why they might want one after so many already had a Wii. Nor was the Wii U Gamepad as revolutionary of a concept as the Wii's motion controls.
Nintendo has certainly done much better for itself with the Switch. Switch sales as of September 30th, 2020 are sitting at 68.3 million units; close to six times the sales of its predecessor. The Switch is Nintendo's most current system so the sales figures are only going to go up from there. The sales of the Switch have no doubt also been bolstered by it's duality as a home console and as a handheld. Consumers are not required to potentially decide between a Nintendo console or handheld this generation and now can buy one system that will grant them access to all the most recent games.
As for sales figures prior to the seventh generation, the NES is not included in the infographic, but it is included in the data later provided by Visual Capitalist, coming in at 61.91 million units sold. Notable is the Gameboy which comes in second after the original DS with sales totals 118.69 million units. Also, despite its impressive category of games, the GameCube comes in second to last place with 21.74 million units sold.
Source: Visual Capitalist