I've been getting that a lot lately as well. I actually got one the other day that was like "I like your channel. This comment is not spam, so don't be fooled. This comment is actually to let the public know that our channel has some exciting new content, blah, blah, blah." It was literally three paragraphs long.
Usually with the sub4sub comments or the people I can tell didn't really come to watch my video, I just won't reply to their comment or give it a thumbs up. If it's an actual advertisement for their channel like the comment I mentioned above, I mark it as spam.
I'm generally not that bothered by them though. As long as I've got a pretty decent number of genuine comments, I'm happy and I think replying back to build that community is beneficial. Eventually the spammers will dwindle away once they've noticed you're not giving them the time of day (hopefully, anyway).
Not sure if that was helpful in any way. That's just what I've been doing.