You can also switch between them: 1st person is more conspiratorial with the reader - letting them into a 'secret' world. 3rd person is viewing events from a distance - emotional disconnection or the inability to do anything about what is unfolding on the page.

If you do not have time for researching topics that you are unfamiliar with, then stick to stuff you know.

A fighter will pick up on errors in descriptions of physical engagements, a soldier will pick on errors in small talk or weapon handling between those of his/her ilk. A parent will pick on errors relating to kids and family life etc etc...