Currently Online 
It's tough to say. I prefer Wii over Wii U, but I prefer 3DS over DS. I prefer PS4 over PS3, but I prefer 360 over One. I didn't play on PSP hardware, but I like Vita.
I'll ultimately go with 8th because of software like Stardew Valley, Spider-Man, Smash 4, Animal Crossing: New Leaf, Final Fantasy VII Remake, SoulCalibur VI, Fire Emblem Awakening and superior versions of cross-gen 7th generation games.
I'm not going to give really any credit to the 8th gen for releases like The Last of Us Remastered because it seems like the 8th generation was so reliant on ports and remasters more than any generation to date. The 9th generation is on track to take that title.
Just about the only thing that could end up putting 9th gen as equal or greater to 8th gen is if you count Switch as 9th gen, but I know we're ignoring Switch on this thread.
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
