I like Izuru the most. Wabisuke is simple but cool to me and his personality is super edgy and I love it. His ideology in his FKT fight was very interesting for me, I wish his character had gotten more focus throughout the story.
Ikkaku has most importance but I like Yumichika the most. His character shows a lot with very little especially when you think a bit deeper. Yumichika says in Arrancar Invasion how the 11th company just fights to death and doesn't jump in each others battles but he himself isn't like that and shows a lot of compassion when push comes to shove.
Yumichika is a fun character with one of the most creative shikai abilities in Bleach. His bankai should be really special if we ever see it. Runner up would be Kira, but that's mostly because of his zanpakuto. Not a big fan of his personality.
Yeah, it's definitely Ikkaku. He's the most interesting, explored, fun to watch, easy to like, etc. He's just a pretty solidly written character who sort of remained low-key prominent throughout all of Bleach. Looking back, I feel like he should've went Bankai (+ Yumichika's true Shikai) against the Quincy.