Primarch who would like being in warhammer fantasy the most and Primarch who would dislike being in warhammer fantasy the most?
I’m assuming you mean that they suddenly ended up there, and not that they were born there. Because the latter would make the entire hypothetical irrelevant.
Magnus would be fascinated by the function of magic and the sheer breadth of new things to learn and study. Also, I think the light college would have him giddy with excitement. So, I think he’d like it the most.
Least? Not sure. I could see a lot of them feeling like it was an annoyance at best to be on Mallus. The thing is that they’d all acclimate in one way or another, because that’s kinda what they do. I suppose it’s possible all the latent aether would make Angron’s nails act up even more than usual. That plus all the slavery would likely upset him. That said, dropping an irate Angron off at Naggarond would be extremely funny.