Switch has been one of the most unpredictable hardware successes ever. Before it came out, I thought there was at least a slight chance it could tank as much as the Wii U. Then, about a few months after its release I figured it would pull NES numbers on the lower end and 3DS numbers on the higher end.
But now it looks to be surpassed only by the DS and PS2 (and has seemed that way for several months to a year or more). I voted for the 135-150 million range. Nintendo's plans for a Switch successor are going to impact the Switch's hardware totals greatly. If they wait until 2025 to release Switch 2, the Switch would probably outsell the PS2 by about 5 million units when all is said and done. If Switch 2 comes out in 2023 or 2024, Switch will probably still come short of the DS.
Switch's peak seems to be 2020, though there is a chance 2021 will be the peak (or close to it).
Lifetime Sales Predictions
Switch: 161 million (was 73 million, then 96 million, then 113 million, then 125 million, then 144 million, then 151 million, then 156 million)
PS5: 115 million (was 105 million) Xbox Series S/X: 48 million (was 60 million, then 67 million, then 57 million)
PS4: 120 mil (was 100 then 130 million, then 122 million) Xbox One: 51 mil (was 50 then 55 mil)
3DS: 75.5 mil (was 73, then 77 million)
"Let go your earthly tether, enter the void, empty and become wind." - Guru Laghima