Root or upgrade to 4.4.2 first? I've just received a new Android phone (an LG G2 D802 32GB). I haven't put my sim card in, or signed into Google yet. I know there is an OTA to upgrade it from 4.2.2 to 4.4.2.

Should I root the phone and then start setting it up, or is it best to carry out the OTA first?
You can do either way. 

The safe method is to update and then root the phone.

But You can also root and then install the ota update. But ota will fail if you have


custom recovery
modified any part of the system like removed bloat, xposed, etc


Still there is  a post in XDA to update ota with custom twrp recovery.