I think Animal Crossing. I mean, when the new Pokémon games (they may be DP remakes or 9th generation) come out, Sword and Shield will sell much less. Instead ACNH is the only game series of this generation, it will continue selling for the whole Nintendo Switch life cycle.

The five weeks after the first for AC sales were around 1.7m if you look at the weekly Japanese sales and compare them to the five week total after the first it shows at this point the majority of sales are coming from that one region as it's like 300k a week which we know from Famitsu estimates is what it has been selling in Japan. This suggests that with WW regions ACNH may have been a lot more front loaded compared to prior games in the series which poses the possibility of the game's legs being a lot more dependent on Japan in the long run than thought.

In comparison SW/SH shipped more but the added shipments in the quarter suggests the 16m has now been sold through, the game was the second best selling non new release after MK8D despite people suggesting that it was dropping off in the charts quicker than expected. In Japan it still sold 310K in the quarter meaning WW regions it did 1m showing it's legs are more across different regions in comparison which could make things difficult in the long run for ACNH to close the 4m gap as it's seemingly falls on Japan at this point.

You're comparing apples to oranges here.  The 11.7M as of March 31 was worldwide shipped (aka sell-in).  The 13.4M as of now is sell-through to customers, and only in JP/NA/EU.  So the total worldwide shipped now is quite a bit more than 13.4M.

Until you can provide those added numbers we can only go with what Nintendo has given for example the numbers in Japan from Nintendo themselves show digital sales are lower than what people thought it would be in the the region.

Yes, but you base the rest of your paragraph on that 1.7M difference.  You can't compare worldwide shipped figures from one time point with regional sell-through figures at another time point and draw any reasonable conclusions from that.

Well when we get next quarter's numbers we'll have a much better idea of where the two stand and what sort of legs they each might have. But I'd put my money on AC passing pokemon within a year and outselling pokemon by a few million lifetime.

The shipment numbers for AC will no doubt be sold through regardless given the game's performance and secondly the numbers given not only will be the bulk of numbers given that these are the 3 major regions and even if we go from the it's only 3 regions angle for these numbers when we subtract the numbers we got from Japanese it highlights what I've observed from these numbers. No conclusion was even given either only possible scenarios and those were derived from the data given.

Pokémon sold 12.28m sell through in 9 weeks according to Nintendo and shipped 16m in a similar time frame

AC sold faster with over 13m in 6 weeks implying that the shipped number is definitely much higher. I could see it already nearing 16 or 17m shipped.

ACNH is the fastest selling Nintendo Game for now

1. ACNH - 13.4 million sold through in 6 weeks

2. Smash Ultimate - 10 million sold through in 5 weeks

3. Sword and Shield - ~12 million sold through in 9 weeks. 

Yes and? You clearly didn't read the full debate.