Pudge and Posada are easily in front of Piazza, who has been terrible for the last two years and was starting to slide before that. Maybe if Piazza could get out of New York, preferrably to the AL where he could DH once in a while...
Pudge was, I believe, 2nd in AB's for catchers last year (behind LoDuca, who is probably being underrated this year and could be a good late-round pick behind the plate), and being in the AL this year will only help that.
Sporting News has Piazza rated 11th, at $10 projected value. I've always been a big Piazza fan in the past, but at this point, his value looks to me to be the same as Lopez and less than Pudge or Posada (that is, I have Piazza rated tied for 3rd, maybe slightly behind Javy).
As far as Javy and Piazza... I think Piazza has a higher upside, but Javy is probably a safer bet. If given the choice between the two, I'd probably pick neither, and hope one of them dropped to me the next round. Otherwise, I'd probably just wait until later in the draft for a LoDuca type.