I have had any issues with iTunes. Google play is spotty, Spotify the same. I have never had any issues with using the iTunes store to find music. If there is not something on there, I always have Amazon.com for backup if need be.
I have used Google Music, Amazon MP3, and iTunes Match. I prefer iTunes, but all my mobile devices are Apple, so it is what works best for me. When I did have an Android phone, I really liked Google Music, on the phone. I hated the web interface though.
Here's my pros & cons of Google Music vs iTunes Match:
Prices are cheaper than iTunes.
Mobile app exists for all mobile devices (althogh the quality of the apps aren't always all that great on non-android devices)
(I hate) the web inteface
You can only download a track TWICE, FROM YOUR OWN LIBRARY!!! (Maybe it's 3 times... I don't rememder for sure).
Store selection is lacking.
You HAVE to use their terrible music manager software. It's really terrible.
Doesn't sync play counts
Works perfect on all my (Apple) devices.
Syncs my play counts (this is important to me anyways)
You can download any of your cloud tracks to any device anytime you want as many times as you want.
Uploading tracks checks for matches in the iTunes store & automatically adds them to you library at 256Kbps (even if the track on your computer is lower qualite (or higher)). This decreases upload time.
iTunes Radio (with annual fee, iOS 7, iTunes 11, available soon)
Annual fee ($25)
No android app
Higher store prices
For me, spending $1 or $2 more for an album isn't that big of a deal, for some it might be.
Both services do not count music purchased in their stores towards your music uploads (I think both have a 20,000 song limit), which is why IF an album is available on iTunes, I buy it there, even if it costs a bit more.