I cannot comment on Spotify, but I pretty much dislike all Youtube recommendations.
I get sometimes different version of the same song again followed by some other song that is also popular but has nothing to do with what I'm listening to followed by something else I "liked before" but obviously don't want to listen to since I already heard it many times. That is followed by a different version of the same song again finally eventually converging on pop music that I generally dislike.
SoundCloud on the other hand sometimes recommends interesting things that I like but have never heard of. Other times, it recommends things that are completely unrelated and that I don't particularly like. However, they're still new/interesting.
My biggest gripe with YT recommendations is that songs I hit dislike on and always browse away from are constantly placed in my autoplay queue. There are some songs out there that I just hate and there's just no way for me to avoid them.
I've never had this issue with Spotify - mostly because of how differently its recommendations work - and it's probably one of the biggest reasons I've abandoned YT for Spotify.
I get sometimes different version of the same song again followed by some other song that is also popular but has nothing to do with what I'm listening to followed by something else I "liked before" but obviously don't want to listen to since I already heard it many times. That is followed by a different version of the same song again finally eventually converging on pop music that I generally dislike.
SoundCloud on the other hand sometimes recommends interesting things that I like but have never heard of. Other times, it recommends things that are completely unrelated and that I don't particularly like. However, they're still new/interesting.