Avoid US Airways - see this thread for details
http://www.pprune.org/passengers-slf...s-airways.html
And I'd avoid Amsterdam as luggage has a tendency not to make the connection.
From speaking to other people, Continental are very good at what they do, and Newark is one of the better US airports to transit through. Apparently they hire friendly human beings at security and border control!
On the BA front - yes, there is a level of uncertainty with regard to the unions and cabin crew, however the time you're going is roughly half term time, and given the outrage caused by the threatened strike over Christmas (and since the union saying they won't strike over Easter) I think you'd be ok. Plus Heathrow is a much nicer place to transit now