Music-wise, it's no contest- the 90s win, not just because more songs are more memorable, but because they were placed more appropriately as narrative interludes and also as artistic set pieces where the animation direction and/or art direction could shine and be associated with the song. Tangled has 90s-reminiscent pacing in terms of song count, placement, and reason but doesn't manage to score any outright bangers (although I love the Mother Knows Best reprise to bits due to Gothel's acting). Frozen's song count, pacing, and their narrative significance is fucking atrocious. And in general, outside of "Now That I See You" and "Let It Go," neither film's animated sequences to these songs are actually memorable or have a truly strong emotional impact. Kids today do not have their own Circle of Life or ballroom dance room yet, nor even something shocking like a Hellfire.
However, there's also the incidental music to consider too of which all films can compete equally, and I feel like this era's been a completely wasted opportunity in that regard. The orchestral leitmotifs of the 90s films are legendary, especially The Lion King's, and they were more likely to embrace the cultural roots of where the films take places, whereas nowadays film in general is scored with bland, interchangeable soundtracks. Like, where are the Nordic instruments and chorals in Frozen (outside of Vuelie)? Where is the opening piece to rival Beauty and the Beast's simple yet haunting piano medley? Do you even remember any background music from Big Hero 6, Wreck-It Ralph, or Zootopia?
Narrative wise, it's a relative toss-up, although I'm partial to more of the 90s films than I am the current ones. They're simpler stories, yes, but that allows them not to be bogged down in the character and narrative twists that have basically served to dampen these current films and add one more layer of cliche', outside of Zootopia of course, which was specifically meant to be a detective story in the first place (I have my biggest problem with Frozen, whose twist with Hans is trite and underdeveloped due to the existence of the Duke while simultaneously undermining how awesome it would've been to have the "true love doesn't exist" thematic be applied in a gender-neutral manner). Because the 90s films are simpler, there's more room to develop the emotional core of the films and execute them wonderfully. There's a sense of quaint genuineness and sweetness out of these movies that I don't get from Disney anymore, aside from something like Winnie The Pooh recently but lol no one saw that.
Ultimately I don't think they're largely unenjoyable. They've been really solid movies, and I agree that their more progressive and topical focus is a refreshing defining feature on what could've been just an era that did nothing more than ape the 90s classics but in a different pop culture environment. Specifically, I still really love Zootopia for its dealings with intersectionality and bias, and Tangled for its childish sarcastic humor and that fucking horse. But I don't think it's just nostalgia talking that the 90s films are still able to compete with what modern technology and storytelling has offered the Disney across generations.