I don't think that telling programs you are ranking them number 1 hurts,
but it also doesn't help much. We have all been burned too many times by
such statements that proved false in the final analysis, so that little if
any weight is put on them. Everybody ranks candidates based on how they
stack up against everyone else (given the subjective criteria being used)
and whether there is a reasonable chance that they will get that candidate.
The big name programs believe, rightly or wrongly, that they can have anyone
they want, so telling that you're ranking them at the top is not very
meaningful. The programs that might be influenced by your saying you will
rank them at the top are generally going to be the ones that you won't rank
at the top, leading to the lack of credibility I mentioned at the outset of
this digression. Do what feels right to you, it can't hurt, but won't
really help much either.