Well my only real exposure to harem MCs are these two, lol. I liked QQ a lot, it's a little slow at first but it's very charming. Fuu-kun in QQ is a good guy, he's not a saint like Rentaro but the show also isn't batshit insane like 100 Girlfriends, so he's more of a real person. You always like him though, at least I did, and you believe he cares about all of them. At the very least it's a fun light watch.
After falling in love with 100 Girlfriends, I watched the first season of KonoSuba on a recommendation and didn't like it much. I didn't hate it but if it wasn't only 10 eps I probably would have dropped it. For whatever reason most of the comedy in KonoSuba doesn't land for me like 100 Girlfriends does. Kazuma isn't very likable, he just seems selfish and gross. The girls are fun, if mostly a little one note. I get the Megumin thing though, she's great and I see why she's so loved.
I recently went back to baby face after more than a decade. It's mostly an attempt to shame myself into getting rid of the second chin.