It depends really. Garmin need to have the approach they have, because their roster is built on foundations of "reformed dopers". No team in the World Tour in 2013 had more publicly known dopers than Garmin. Not Astana, not Movistar, not Katyusha, but Garmin, believe it or not (Danielson, Dekker, Millar, Rasmussen, Vande Velde and Zabriskie, plus Klier confessed mid-season and now Hesjedal post-season too). A Sky-styled ZTP would not be possible for Garmin.
Sky's ZTP is a very noble idea if stuck to, but is nigh on impossible to stick to, because you never know when dirt could arrive on somebody who's been around the sport, and the need to have riders and staff with experience was made painfully obvious during their growing pains in the 2010 season. However, at the same time, there's a difference between picking up riders who dirt subsequently appears on, and picking up a rider like Mick Rogers, who had been named as a Ferrari and as a Freiburg client prior to signing, and was subsequently named as a Ferrari client in the Reasoned Decision. As a new team, however, they at least had the option of setting up a ZTP; if a team that has been in the péloton for decades, like Lotto or Movistar, were to set one up, it would be absolutely ludicrous, as almost the first thing that would happen would be the entire team top brass get fired due to their participation in the dodgy old days of the 90s. I just think that a genuine zero tolerance policy is absolutely not possible in today's péloton, even if Sky were genuine about it, which is in retrospect difficult to believe when they hired people like Sean Yates.
The problem with both approaches is as spalco acknowledges - they are fine as long as they are genuine, but both carry the whiff of being disingenuous at present; a number of Garmin's confessors are only confessing when their names would be being made public anyway (Hesjedal, Klier) or when fingered by others, accidentally or deliberately (Danielson, Zabriskie, Vande Velde), and also the confessions have been typically very limited in scope and not wholly believed, whereas Sky's zero tolerance policy has proven to be as impermeable as a sieve and has seen some hasty backtracking and jettisoning of riders that don't fit it, and the layman could have told them didn't fit it and if the team had conducted due diligence as they say they do (attention to detail, guys, attention to detail) they would never have hired them in the first place, which makes the Sky management seem either disingenuous or incompetent.
The Astana "we hire who we want when we want" approach may be repulsive from an anti-doping perspective, but at least what you see is pretty much what you get and you don't get all these BS rationalisations or tearful "I was lied to" and "I only did it once, outside the statute of limitations, and I didn't like it" Paul McCartney-talking-about-drugs like confessions.