The part Republicans like the least is Requiring district lines be based on the total population of the state, and require the state to count all residents not just citizens. I understand that this is required by the U.S. Constitution so only counting citizens is fundamentally unconstitutional. Of course, depends on how you interpret the constitution but the literal language is clear. You can imagine why the Right is so opposed. Personally, I think it has many practical benefits, but it also obviously benefits Dems.
