Pokemon 2018, Smash LT
Pokemon releases earlier and while not an entirely front loaded franchise it is a lot more front loaded than Smash which only has 1 game per console. The Pokemon game on Switch after Lets Go is already announced for 2019.
While I can see Pokemon selling 10m+ LT (maybe even the 15m Pokemon usually gets, i dont think the GO mechanics will hurt it too much considering all the positives it has going for it) I feel like this new Smash will be the best selling in franchise history so it doesnt matter.