I love Haruki's route and I think its the best, but I'll have to replay it to give more detail since it's been awhile, I have also been really enjoying Keisukes route so far, if you want more detail about that then ask and I will.
My personal favorite is Jun's. I will do anything for that adorable tiger. I have medical complications the same as Jun and it's rare to see a story that just gets how it feels. Sometimes you're just in a ball of emotional and physical pain and seeing that represented so respectfully and thoughtfully is incredible. Definitely my personal head-canon, canon route.
I thought they all had their aspects that made them unique and gave the characters their own stories. Personally my favorite is Keisuke, but that's just because I just can't get enough of the hare, but I think all of the routes have their own unique strengths that make them very difficult to compare to each other in the sense of which route is the best.
Shoichi used to be my favourite, but after Haruki became a route, he's hands down my favourite now. His character is just so interesting to me and he's hot ofc. I am really excited to see more of him and how his relationship with Yuu is gonna develop. My favourite part is seeing him slowly warm up to Yuu over the course of the story and I hope we manage to help him see the world in a better light.
While all the routes are unique and I love each one because they are all great, my personal favourite is the good path of Shoichi's route. I'm firmly in the Yuu-Sho shipping camp, and his route is the canon route in my head-canon. I guess that means I love the best friends to lovers trope, lol. My ranking of the routes on a scale of most favourite to least favourite is Shoichi (the good path of his route is the best in my opinion, and I'm looking forward to reading more), Haruki, Keisuke, and then Jun.