When I look at the first drawing, it feels disorganized with the leaders, but the second option appears doesn't seem to work with the text (sometimes) crammed in a tight area (i.e. the 200x100 & 200x150 ducts).
I have seen it done both ways on various projects ... but probably the best way I have seen it done is with a schedule in the drawing and an identifying mark, similar to how doors and windows are identified on many drawings.
If I have to choose one of the two though, I choose the second drawing, but maybe adjust the text height slightly to maintain readability.