You know what's really strange? I thought you hated that picture, but now it's your avatar.
Anyway, I honestly think both are kinda crap now.
Soundcloud was great before it got rid of embedded sharing into social media like Facebook, and groups. I cannot, for the life of me figure out why they thought getting rid of groups was a good idea. There is also the fact that it is plagued with bots, or people who feign interest in your tracks and page, only to unfollow and unlike you if they don't get a follow back almost immediately...
YouTube is the superior platform in the sense that how you can present your music is a lot better. You can get great After Effects templates and all that jazz. The downside is that YouTube expands more rapidly than our own universe, and it's extremely difficult to bring in much of an audience. Worse still, is that in the last few years, Youtube has become a haven for SJWs and Neck-bearded, fedora-tipping "skeptics"; it's a political cesspool. But YouTube sides with SJWs, and as I've seen videos demonstrating, Youtube will demonetize your videos and make them harder to find even if you associate with someone who is known to disagree with their politics. Not sure if that applies to subscribers, but I doubt it.
Back around 2010 - 2013, both Soundcloud and YouTube were absolutely amazing for sharing music. Both have fallen from grace, and nothing has really risen to the challenge of filling the void.