the most secure is to have an unlocked phone that you can remove all the bloat that is included by you provider.  it also provides ways of backing things up that aren't possible with a locked phone.  maybe to late for you, given you already have a phone, but check with the guys at xda forums for information on how to unlock your phone, if possible.  

if an unlock is possible, be sure you match the exact phone and service used.  this can be tricky, so be patient when gathering info and do you homework.  i prefer the 'stock' roms that have bloatware remove.  if you can get root access you can stop anything, and not change your rom.  i stay away from the user made roms because they seem to be less stable.