One is easier, the other more effective.

I like to answer individually.

It would be nice it we got notifications when people commented in those subcomment boxes.

I answer individually.

Silvia - I think it would get too time consuming to comment or answer a comment on everyone who commented on your post. I already spend too much time here on AR, so I try not to do it very often.

I do not tag the writer in a comment ever. If I want someone to see my comment I will tag even with the new feature.

It's easier to comment right under the post.  However, you don't get any points for this type of comment.  

Not tagging nearly as much as I used to but I figure that any response is better than none so it varies.

Should be below. But I have seen tags addressed to multiple people also.

The problem is that the person is not getting tagged on the comments.  so, they don't see that...hopefully, they will fix that soon.

I generally only tag people when I feel they need to be tagged e.g. if I am answering their q or I have a q for them or if they wrote an exceptionally amazing answer.