Mastering by a human is essential!....
Don't get an online algorithm to master your music. It has no empathy or emotional intelligence and hence no idea how to help project the emotional message of your music to the listener. You will end up sounding substandard and generic.
I've been mastering for as long as I have been producing music (since 2003) and mastering has seen a massive change, both technologically and stylistically in that time. The main priority now (thankfully!) is to make your music jump out of the speakers, bounce, dance and knock your socks off, as opposed to attack you with loudness to make sure you are beaten into buying the record.
I can master for all the different online music vendors such as, Spotify, Soundcloud, iTunes, YouTube, etc (who have a very subtly different approach to how they playback and in some cases process your music), but also, I master for traditional formats such as CD.
To the right hand side of this page you will be able to listen to some of the records I have mastered. Let me know if you think I can help make your record sound great!