Is there any advantage or disadvantage between taking the above airlines from NRT? Will possibly fly from the US on American to NRT and then continue to BKK using one of the above. Have never switched airlines before during a flight. Would I be able to check my bags through from my start in the US? Would both airlines be in the same terminal that I would land in coming in on AA?

The AA default for flights to BKK is on JL's Jalways. Now that JL is a part of the One World alliance you would probably earn AA miles on those flights. If you're interested in F seating, I believe that there is only one JL flight to BKK that has those. When flying DCA-JFK-BKK on separate tickets for AA and TG I have never had a problem with AA interlining my bags through to BKK. Although I'm a big fan of TG, for simplicity's sake I would fly JL. In fact, I would try to shift my US-NRT flight to an AA codeshare on JL. Much nicer service.