I didn't enjoy Feylin; from the beginning it seemed stereotypically fairytale & (gradually) so unhealthy. Feysand def pulled me more into the story on the whole. I do think both relationships were vital for every character involved, though. I think Feyre needed the experiences she had w Tamlin just as much as she needed to find Rhysand & finally step into a relationship that was healthy & loving. I'm also supremely relieved that Maas didn't just offer up a bandaid for Feylin but that you do see a lot of growth for both Feyre & Tamlin bc of how things went between the two of them. It's a slower process for Tamlin but you do see that he has some good there when his anger & ignorance stop eclipsing it. I think it's just a matter of him needing someone to stoke that for him; he was too naive and entrenched in his own person to really see Feyre as anything more than a possession that was his to mold.
I think Feysand was by far the best relationship ever... like Tamlin was not the one. i do believe everything happens for a reason but i think Tamlin didn't accept all of feyre... if your gonna love someone you don't get to choose which parts you love "dorian". and i think feyre changed like all people change and tamlin didn't accept it and that is what made me dislike Tamlin so much.. but also seeing feyre slowly fall apart and tamlin had no idea (how idiotic)