Hi Smokie,
In the event of job losses I think that the Airbus rating would be more valuable in the short term, at least until everyone starts flying 400 freighters where it might then even out a little bit. Given the choice now, I would rather be on the Airbus because it is an easier fleet to justify commuting to work on. The Airbus generally does longer trips, thus slightly more days off between work patterns. A possible downside is that heavy crews are often carried, so it might turn into a toss of a coin for a sector. All 400 crews a pleasure to work with, and I am sure the same goes for the 340. Hope this helps a little.
Rgds.