I recently finished the Sound! Euphonium novel and really enjoyed it. I'm a massive fan of the anime, and whilst I did like the book a lot, I still feel the anime is superior. I think it did a better job at developing its side characters, such as the wonderful episode where Kumiko has to try and cheer up Hazuki, and the anime also made some small adjustments for the better to existing scenes such as Reina performing the trumpet on top of the mountain instead of just sitting up there and the way the solo part was decided during the re-auditions. That, and the fact the anime can actually let you hear the music, which gives it a big leg up. Still, I did quite enjoy being able to see things strictly from Kumiko's point of view and hear her internal thoughts a bit more, and it's also a lot more concise if that's more your jam. Despite preferring the anime, it's not by much, honestly, and I ended up totally adoring both. Can only cross my fingers that we get the sequel book soon.