Yup primedice is the most popular bitcoin gambling website out there. Take a look on the weekly wagered stats of gambling sites :
https://dicesites.comPrimedice is on the top with 7619 btc (5+ million dollars) while the runner up Betking have 4.5 times less amount wagered than primedice which proves no one is near the popularity of Primedice
When discussing about the trust, then it's up to the user to decide. For me it is the most trusted
Private bankrolls allow for max stat manipulation so their numbers are meaningless. They haven't shown to be untrustworthy when it comes to paying out. That's about it.