>>58922199From a purely visual standpoint. Gen 5 easily has the best menu for everything, be it either BW or B2W2, it was also cool how B2 and W2 had different colours the menu, even if the latter one looks not as good as the former. I really like the Item menus for both out-of-battle and in-battle, the Pokédex, the Party screens, the battle display for bottom screen and top screen. It looks cool seeing the six HP bars there in Triple Battles with the six Pokémon, makes things look all complex and strategic. Gen 5 is also the first gen to have the animation for an Ability activating, instead of only text, and no other Ability activation animation has ever come close since. But some of the menu's aren't as good, like some of the ones from the C-Gear.
But gen 6, is a good second place, some of the things I said from gen 5 apply there too. For gen 6, notably, the PSS has really good menus and as
>>58922204 said the Pokédex. The PokéNav Plus makes things even better for gen 6. And it was cool how in ORAS that Super Secret Bases and Pokémon Contest Spectaculars both had their own unique visual style of menus to fit their own vibes.