The answer lies entirely on which build version is in the phone. The only known rootable version is 2.17.605.2 (a.k.a the "First OTA").
If your phone(s) have this build, do NOT allow the latest OTA to install. Root them immediately. Several methods are available, just refer to the resource index for your desired method. I highly recommend s-off, regardless of which method you choose.
If you have the prior build version, 1.43.605.3, then MANUALLY install the 2.17.605.2. RUU, Root immediately thereafter. Make sure you kill the ability for the OTA to be checked/installed.
If you have the latest version, 2.19.605.2, it is unknown at this time how to root...