I think you will find that if you want 'International' style first class, you will need to target the widebodies (767, 777, 747).

To be frank, if you are wanting to go non-stop, then you choices seem limited to DL, AS or B6 (which has no first).

You also haven't said whether you care about BA Miles and TP's? Is that important to you or is it just best first class?

If it is BA TP's then have a look at the ulitmate guide sticky and book yourself a Y-UP TP bonanza.

If you want best First, then you need to decide between UA, AA and CO's BusinessFirst, but you will need to go via somewhere to get on on an internationally configured aircraft.