I'm nostalgically attached to NIL, but my taste appreciates DIM more. But both albums have their pros and cons, and are still strong releases in the band's discography.
NIL feels a bit more organic overall since it's not constrained to a specific aesthetic like DIM - basically, there's more variety. DIM on the hand seems to have a clear-cut vision (from the highly stylized PVs, to the artwork, to the incessant use of SE tracks in an attempt to guide you through that vision), and as such, the songs on the album don't step too far out of line from that vision. They managed to achieve an amazing sense of cohesion with DIM - almost as if the album tells a story. Personally, I think that ambiguous, yet palpable "story" of DIM is what draws listeners to this album over NIL - which I think was also a good effort, but feels more just like "another VK album", ya know?
That's not to say NIL isn't worthwhile. With the atmosphere of DIM being so thick, it's easy for that album to feel oppressive, while NIL has a kind of levity permeating throughout it. Another thing I enjoy about NIL is the fact that there are more solos and much more going on guitar-wise, while DIM is riddled with breakdowns and mirrored-chugging (which gets old fast especially when there are 2 guitarists). The guys of gazette may not be super-technical guitar/drum-gods, but they can rock out with their instruments when they want to and I would have liked to hear more of that in DIM. In that sense, many of the songs on DIM felt a bit sterile. Tracks like "13STAIRS[-]1" and "Nakigahara" - while great, presented a slew of musical opportunities for the gazette that they failed to capitalize on. "Nakigahara" was begging for a solo or some sort of instrumental fuckery, but instead drug on for like 3 minutes too long. "13STAIRS[-]1" was something new and fresh for the gazette, and still stands out in their discography today, so they really could have experimented a bit more if they wanted to. And the gazette doesn't have to get all progressive or anything - even if one song on DIM had an instrumental section on it like NIL's "baretta", I would have been more satisfied!
But with everything said, I still prefer DIM overall. Despite it's flaws, the album and everything surrounding it were curated so fantastically, and that's not always an easy feat achieve - in vk or anywhere else.