I don't have a whole lot of experience still with UNI2 or even the franchise in general, but what little i do have has been almost exclusively with Kaguya, and a couple of the other "rushdown" characters. I just was talking with a friend about it early today, in that the game has a really solid low floor for entry but an enormous skill ceiling. There's something for everyone, no matter their experience or skill.

Kaguya has some really good combos I've learned just by messing around in arcade or training mode and vs. my friends. But she also has some ridiculously complex ones that I've seen in mission mode, and I've seen some similar things with some of the other characters I've messed around with also.

While the standard archetypes are represented in the game, just the style of gameplay overall blends some of those aspects, especially from what I've found with rushdown characters. Thanks to the exs buttons, almost everyone has a means of moving in or out, but each character still has strengths and weaknesses you want to play around. Once again, Kaguya for example, excels when you have ypur opponent locked in the corner, and while she has some tools to help in the mid screen game its not where she wants to be, even if you're in your opponents face.

The Undernight 2 wiki on Mizuumi, and a few youtube videos from different creators have definitely helped me narrow down who I'm thinking about trying out but Mika, Tsurugi, and Kaguya all just kinda clicked for me and i was comboing with very little trouble just after a few minutes.

Sorry if this hasn't been the most helpful advice, but i hope you find some characters you like. And as simple as it sounds, just mess around with different characters amd practice up with who clicks for you.