From my experience, first of all from some time there is new feature in YT, you can set whose comments are going to hit top. Default is as far as I remember 500 subs.
Next thing that I have seen someone has posted is that old accounts have higher priority in hitting top in comments section.
Another thing is giving upvotes. One year ago I could without any proxy put 10 (maximum) upvotes to make my comment hit the top, add some sub comments and it almost always was on top. Now if you put upvotes from same IP than you will get your comments ghosted for some time. Only you will see them. If you use proxy for every single upvote put some sub comments you will not hit the top even with that. The priority of subs count and activity on owner channel will make your comment far far away from top.
Since today I havn't managed to find a proper way to make comment hit top. If someone with lots of subs or even owner comments your comment that it will hit top easily, without that I highly doubt it is easy.
