You should really do LAX-JFK on AA, not BUR-JFK (AA T4 is well run but understand getting to/from LAX can be a challenge.) If you are EXP there are decent shots at an upgrade. Worst case you get E+ for free at booking (assuming you make at least PLT) which is already more than what Mosaic can give you (no upgrades and E+ only at checkin based on space available)