I don't know too much about the mainstream but I can say that the 2010s were a GREAT decade for doujin music
Taishi in particular had a meteoric rise after his 2000s work with CODE ZTS LABEL with his new compllege label and it's really hard to choose just a single album... I might pick the original "Phant" album. There's only three songs but you get a showcase from the entire Holy Trinity of Trance: Taishi, zts, and Nhato. "bluefieldcreator" might be Taishi's magnum opus (others might disagree) and "freeflakes" is a great entry from zts, my all-time favorite doujin artist.
zts didn't have an album I'd pick this decade, which is fine since his late 2000s work is enough to pack an entire career, but his work in Umineko is still untouched to this day. He also made some absolute bangers for Mashiro Witch (rip), like blackstarlight and lingering affection:
He also did an absolutely stellar job with "point at infinity" for the Mashiro Witch x Umineko collab... I can't find a good rip on YouTube so I might upload it myself sometime.
Outside of the trance sphere, OPHANIL by KOSZONTO was probably the best doujin album I've come across in the 2010s. It's just... magic. The album is operatic so listen to the songs in order --- the whole thing is only 20mins or so and totally worth it.
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Not a "best album" but I wanted to give a shoutout to yogurtbox for "Tree of Knowledge", an OST for a fake PC-98 game, using the YM2608 soundfont. They were inspired to start the project after listening to Ryu Umemoto's brilliant EVE: BURST ERROR soundtrack and it really shows. I would be really interested to hear a followup to this after they have the time to sit down and play through the entirety of YU-NO, undoubtedly one of the best gaming OSTs ever.
Standouts from "Tree of Knowledge" are Opening, Schedule, and Evil Spirit. 'Opening' in particular reminds me a lot of YU-NO's opening: