Upgrade via stock or flash TWRP backup

Hi guys,

I have done a TRWP backup of the system partition after I upgraded to Android 5.1 (Brazil) but unfortunately I lost that backup stored on my OTG device so my question is how is simple or safer to do:

1. Take a someone backup (if somebody makes it) with Android 5.1 made by TWRP and restore it on my device.

2. Flash Android 5.0.2 without modems, GPT, motoboot and just the system partition and then upgrade via OTA.

So 1 or 2 ?

Thanks !