>>57193138We can discard gen 1 to 5 as the easiest, seeing as they don't have any friendship derivative mechanics nor easy QoL meant to trivialize the game like super and hyper training.
With that in mind, I'd narrow down the contenders to:
>XY>Let's GO>SwShMy reasoning for disqualifying the rest:
>ORASAlthough ORAS suffers a lot of XYs faults as well as RSE's, and even goes out of their way to get you a free mega Latios/Latias, it's worth mentioning that those two are not great against any of the Elite 4, and by the time you get them they are also not effective against any of the remainder gym leaders. You can trivialize the difficulty of the game past 6th gym, but it also has Elite 4 rematches.
>BDSPAlthough it has a lot of modern QoL, it also provides upgrades to the Elite 4 rematches, with it still being as solid as it was in DP. Game also has some extra challenges like the Shadow Giratina boss.
>SM & USUMAlthough not that hard, Totem fights are probably harder than most gym leaders in the series, even with Z-moves they are hard to get rid of, usually have stage hazards in their favor especially weather and have omniboosts on top of reinforcements. Mega evolution not present until post-game.
>SVVery easy to get over levelled and predictable gyms, however it has a handful of hard fights worth mentioning like Champion Nemona, Sada and Turo, Ogerpon, Drayton, Kieran, and everything that gets updated once the DLC is done averages the lv80