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I need to use Google+ more had me co fused first time I tried it lolTwitter is what I use the most, although in terms of exposure I think it's not the greatest one.
In Google+ (yes, I know it's not the best example of well-design social network), if you engage with several of its communities, you may get some views and subscribers without having to ask a user to promote your posts or anything similar. However, depending on the size of your channel, it could happen that your posts never made it to the top of the community page (since the post order is a strange mix between time lapse and popularity)