Beast wars comes to mind. "truck not munkey!" was all over the transformers sites with a group of fans who hated optimus not a truck. Group hated animal forms over car forms. Today beast wars is pretty loved by most transformers fans. Ironic the beast wars fans had their turn with beast machines that had so much backlash the writer got death threats from some awful fans and vowed never to do anything transformers again!
https://tfwiki.net/wiki/Trukk_not_munky
Then there is wally vs barry and hal vs kyle from dc over the years. Ironic thing is none of them are the originals!
Some ninja turtle fans hate the jokey 80s turtles over the dark and gritty comic ones and dragon gt got alot of hate in its day from some fans.
Teen titans go is pretty hated by some.
Star trek vs the next generation lead to fights in the 90s. (al even spoofed that in his white and nerdy video)