Cons of Spotify is definitely the integration into the larger Apple ecosystem.
Cons of Spotify *Can't do voice search with Siri for music *CarPlay - I don't have it but I tried it in a friend's Volvo and last year it didn't have any controls on the screen. (Didn't test Siri controls *Apple Watch integration is only through now playing. (Skip/Pause/Play Volume work)

Pros of Spotify *Playable on a wide range of other non-apple devices. (May be a con if you are totally bought into Apple) - Amazon Echo is my biggest - On the Echo you can do voice search for Spotify music. To play Apple Music - you need to connect to bluetooth to the Echo. Spotify is pretty much on any IOT device out there. (other than your toaster but I didn't go to CES so I'm not 100% sure that is still true) *Discover music through friends (Facebook) *Can put any song into the Djay app *Honestly I switched over during the period when Apple didn't offer a subscription service - since I have a bunch of playlists now it would be hard to switch back.

What I can live with *Siri voice control works with the player (Play/Pause/Next/Previous all seemed to work for me through my AirPods) *AirPod support - seems to work with whatever is playing - i.e. - Siri to voice control (above) and taking one AirPod out of my ear pauses Spotify *Now Playing App on the Apple Watch is good enough - Skip/Pause/Volume is available.

TL;DR - if you are all Apple stick with Apple Music.