Spotify no doubt! I have been an avid fan ever since I was first introduced to it my Junior year of high school (Circa 2012). I bought the Student Spotify Premium and never looked back. By the time Apple Music came out, I was so used to Spotify that I never even considered it as an option. I still don't and won't unless something drastic happens with Spotify.
At the moment, it's 100% Spotify for me. While I haven't used Apple Music extensively, I'm very attached to my playlists and the way I have things organized. Spotify is also the streaming service choice for most of my friends, so it's easier to share things with them than if we all used different platforms.
Additionally, platforms like Apple Music and Tidal have an elitist air about them that I find unappealing. I think it's kind of lame that artists will exclusively release content through a single service.
Personally, I've tried both. However, I have reverted back to using Spotify as it seems to be more intuitive to my music taste and the overall functionality of the app is a lot better. Apple Music was very simple to use but almost too simple and didn't have the same relationships with artists to leverage exclusive music/content. I can see it changing in the future but for now, Spotify is what I'm using.
Definitely Spotify. I've had Spotify Premium for the past 5 years, since I started college. The last time I used Apple Music it cost 99 cents per song (is that still the case??). I initially switched over when Spotify began offering free music, and have never looked back. I love being able to search for existing playlists and follow my friends playlists. It takes away a lot of the stress and pressure of making them on my own. I'm also a big fan of the curated Discover Weekly playlists on Spotify. That's how I find most of my new music.