DJBenz
Loving YTtalk
Even though I understand what people are saying about Reddit being a very critical place, I have had the most success with Reddit out of all of these options. For my channel's niche, it's very easy to cater to subreddits specific for the particular games whose music I'm covering.
The results of this poll will be skewed, because not everyone will have used every option to its fullest advantage. Reddit is a tough nut to crack, but if you do it, it will obliterate the traffic from any other source - guaranteed. Don't get it right and it'll be a nightmare though. It's the most difficult network to promote on, but it will yield the biggest reward by far.