While you still can...stick with TWA. Buy your tickets thru lowestfare.com and get 25% off. Post miles to either TW or AA.
If merger goes thru, all miles will end up with AA, anyway. If posting miles to AA, TWA can count as Q miles.
25% off business fares can really add up quick! Take advantage of it while U still can. Just MHO...FWIW.