I think both Yuri and Yaoi can be entertaining depending on who writes it. I don’t think the toxicity of the relationship or believability of an antagonist has anything to do with either.
If the author can’t write believable side characters or a good plot, then that’s their problem. The genders of the main couple shouldn’t be associated with the quality. Though I can see how one could form a bad impression because of that. The majority of Yuri that I’ve read consists of:
Wow! I feel attraction to another female! That’s INCONCEIVABLE!!! Let’s have sex!
Either that or it’s just a boring, overly cliched love story except with two girls. And the same thing can, and definitely has, happened with Yaoi too.
The yaoi or BL that I read have plots that I find entertaining, and while I enjoy BL itself in the first place, I wouldn’t read it if the plot was boring.
I myself haven’t found any Yuri that matches my taste in plots (*cri cri*(well actually there is one that I think is really good)) so I naturally prefer BL. At the end of the day, if you enjoy Yaoi solely for the sake of it being Yaoi, then you’ll always prefer Yaoi, and vice versa.
I suppose what I’m saying is, the genres of both Yuri and Yaoi shouldn’t all be put into one box. There’s Yuri that’s much better than Yaoi, and Yaoi that’s much better than Yuri.
But if we’re throwing the whole, ‘depends on the plot’ idea out the window and the question is asking whether you prefer women in love or men in love, then fuck it, Mo Dao Zu Shi is the shit.