I agree Cucumber is the most fun MC to follow with his screaming internally but acting cool outside
I actually really liked HOB romance because there were no stakes. I mean, if I was reading ecause I wanted relationship drama that would suck, but it was nice to see a romance where was no strife since that's rare. It was fun but peaceful, which worked well give in everything else the plot had drama and angst galore.
Maybe because SVSSS was her first work, it's clear the writing wasn't as good as the next two, and the length was also much shorter. Because of those I didn't much like the romance: I finished it without feeling like I was watching a couple get together, but more like Cucumber accepted his fate of being with the Protag because he was responsible for turning the guy homo and he was unstable. I wish she'd done a better job of showing Cucumber actually develop feelings for the Protag, especially BEFORE he became aware Protag was going nuts out of love for SHIZUUUUN. So for actual relationship 'drama' I'd go to MDZS, but for comfy relationships HOB
I wish author hadn't stopped adding more than one homo couple per plot after SVSSS
Plotwise (non romance I mean) I also think it really depends. HOB has an unfair advantage of being so much longer and thus having more space to expand on plot and add subplots to flesh out stuff. That said, for satire obviously go SVSSS. For misunderstandings go MDZS and for big scale epic over human nature and goodness, go HOB. For plot that is more nicely tied up with more intricate detail, go HOB.
For side characters it's hard. All three had great side characters but again, HOB had more time to flesh these out and thus wins in my heart.