Back at it again.
Silent Sinner in Blue
This is the other experimental PC-98 EP, and thus the informal companion to Perfect Memento (even following the same tracklist structure of two originals and one remaster). In comparison, these arrangements are a bit more standard, following familiar progression structures. Youkai Space Travel is my recommendation as possibly the closest we'll ever get to a PC-98 music collection.
Touhou 10.5 ~ Scarlet Weather Rhapsody
This is where Akiyama properly established himself into the legacy of Touhou, although I find he rarely gets the credit he deserves for it. I'll get The Ground's Color is Yellow out of the way now; it is still one of his most infamous compositions, and serves as an excellent example of his style and its strengths. The rest of his collection is something of a study; multiple tracks reuse motifs from each other without any apparent connection otherwise, but other tracks are allowed exclusivity in their arrangements. There's a consistency throughout that may make quickly distinguishing between tracks difficult, but no track is without its unique touches of instrumentation. I pick Drunk as I Like for my secondary, though it's a close call. There's a bit more to the honorable mention this time, too; one might expect attention drawn to ZUN's contributions, but while his style has settled since the last fighting game, I find I prefer Akiyama's arrangements. It might be cheating to consider Crimson in the Black Sea ~ Legendary Fish (Arrange), since it's exclusive to the released OST and not part of the game itself. Nonetheless, I consider it one of the many overlooked contributions of Akiyama, and would thus like to draw attention to it. Alternatively, I'm especially fond of his rendition of Aya's theme.
Touhou 11 ~ Subterranean Animism
Feels like the gaps between main game entries are getting wider. Touhou 11 is where I first started noticing the stylistic uniqueness of each game, independent of ZUN's personal style. This collection is characterized by darker sounding arrangements, both in instrumentation and progression structure (and even motifs, to an extent). You can usually source a track from this game by the sound alone, even if you can't recall it completely. This is technically true of previous titles, but this entry accomplished it in a most noteworthy way nonetheless. Awakening of the Earth Spirits is my favorite menu theme of the series, not so much because it accomplishes anything special with the leitmotif, but more due to the atmosphere captured in the track. Second choice is more difficult (as per usual of late), tied between Green Eyed Jealousy and Satori Maiden ~ 3rd Eye. While the former was an early favorite, the later grew on me over time, so take that as you will.
As a side note, Hartmann's Youkai Girl is overrated; not by any means bad, more my personal U.N. Owen was Her?.
Grimoire of Marisa is an especially egregious example of ZUN's EP practices; it has only two tracks, one original and one remaster. If one is at all a fan of the Seihou soundtracks, there is a good chance the original was perfectly satisfactory, in which Magician's Melancholy is the default pick. I do like this track, but its presence in this list seems somewhat hollow under the circumstances; I would personally have preferred ZUN to have included both tracks in a music collection (they would have been a perfect addition to Volume 5.5, if only its release was closer).
I am again out of time, and I'm still stuck in the first modern era.