My ultimate favorite would be X JAPAN, to be more specific X (w/ Taiji on bass). IMO, X on their heydays were really a collection of best (Japanese) musicians in their instruments. It is just sad that they are not quite active even after reunion, given all these circumstances happened to hide, YOSHIKI, Toshl and even PATA. Still waiting for new album.
LUNA SEA tracks are frequent in my playlist too. Compared to other visual kei groups, they're just like a all-rounded cool kid in the class. Still going strong with same line-up since their formation.
SCANDAL - adorable and talented girls.
and the wolves, MAN WITH A MISSION. They're just unique among contemporaries - both visually and musically.
YMO, neither fits to J-ROCK or J-POP specifically, but these grandpas are classy maestros. Though Olympic is postponed, I'd love to see them in opening or closing ceremony.
Other favorites that I love and listen (but not quite to the degree of above 4) - BABYMETAL (prefer the one w/ YUIMETAL), back number, BAND-MAID, B'z, FLOW, fox capture plan, Kankaku Pierro, KOKIA, Kyousuke Himuro, LOVE PSYCHEDELICO, RADWIMPS, Superfly, Utada Hikaru, and ZARD (her anime tracks are gold, RIP T_T ).