Full album has to be Twicetagram, partially by dint of it being the only one I have.
As far as EPs are concerned, I'd probably have to give it to Dreamcatcher's Alone in The City. Trap and Wonderland are two of my favourite DC songs so far.
Perfect Velvet by Red Velvet. The whole album is literally such a masterpiece. I recommend listening to "Kingdom Come"! And my second favourite would be Crush by 2NE1. I love "If I were you"! ❤
In terms of kpop merch, the CHEER UP album for TWICE has some nice goodies But in terms of their main song and side songs, I'd say COLOR*IZ/La Vie En Rose album from IZ*ONE