School Rumble both Anime Adaption and Manga.
Anime Adaption cause Third (and last) Trimester was shortened to just OVA, making it sudden and extremely hard to follow if one did not finish the manga. I understand that they started to screw up near the end of season 2 since they ran out of content and used fillers. I believe they should've weaved the fillers through season 2 but definitely postpone season 3, so they could make a proper season (cause there was enough content at the end to atleast make a 12episode).
Manga cause that ending was so bittersweet. It felt more bitter than sweet that Tenma went to America and Harima went on a road-trip. I hate it even more that Karasuma suddenly admitted his love, Harima had to push Tenma to Karasuma, and everyone accepted Harima as someone who loved Tenma no matter what...
But the thing I hated the most was how logical that ending was!!! I can't refute the ending as the one true ending. The character development, the events that brought them where they are, the showcasing of each person's desires. Harima loved Tenma from the start to the end, Yakuma crushed on Harima but she knew he loved her sister. Karasuma wasn't impossibly dense but had a reason to shy away from Tenma, there wasn't any time for Tenma to actually fall in love with Harima cause of all the misunderstandings, and Eri was Eri.
Yakuma is still best though.