Personally, I hate iTunes and it's overall navigation and layout. Pandora, iHeartRadio, and remember LastFm? I liked those apps for general radio and discovering new music based on my tastes... but I find their audio quality and overall presentation not suited for me. Maybe I just haven't ventured far from Spotify since i first started using it... so I may be jaded as to what the other options offer nowadays.
Winter 2013, I had just moved and my PC was temporarily not connected to a battery backup... so of course lightning strikes and fries my HDD. 15 years of MP3s, FLAC, AAC files all a mess and partially lost. That's when I leapt into Spotify and haven't really looked back. Paying for premium allows me to playback at 320kbps and download my songs and playlists for offline use. It has most everything I listen to, and indie stuff or music that I don't find on there I can upload onto my own Spotify from other sources. It has radio, albeit not as good as Pandora perhaps, but I prefer my own playlists anyways. It's pretty much everything I need it to be.
I have Amazon Prime... which includes music. So it seems rather redundant that I pay for Spotify. Regardless, I still prefer Spotify overall and so I pay for it.
My two cents.
(EDITED FOR WORDING AND GRAMMAR)