I have personally used both, but I stopped using SoundCloud for years, and started uploading frequently to Youtube like a year or so ago
Both have their pros and cons, but Youtube definitely has the upperhand in reach, or at least for me, I got a lot of views and comments because of the arrangements I uploaded there, and thumbnails and entertaining visuals help
Although one difference I had while using both is that I had a lot more success with original music using Soundcloud, whereas the success I had with Youtube comes from arrangements of other music (note that when I say "success" I'm talking about a relative/moderate success). However to get people checking my Soundcloud I had to post on 4chan, and I didn't really find any other ways of promoting my page, but probably chalk that up to me being very noob-ish in promotion in general
But yeah, I think Soundcloud is a good site for original music, if you upload original music to Youtube, don't expect much people to find you, but it's still a good way to build a fanbase through the likes of arrangements and stuff, and then use it to promote yourself
My conclusion is to use both, you don't really lose anything, if you're not sure about the visuals for Youtube, it's really easy to put some basic background in Sony Vegas along with the music, more attractive visuals always help (like having yourself playing, or any picture that would attract viewers in the thumbnail), but you can easily start with that, maybe learn to do some basic effects in Adobe After Effects so you can have something moving in the video and it doesn't get too static