Proposed New York Trip March 2013

Hi all,
I am thinking of going to stay with a friend in New York in March next year (proposed dates 14th - 21st March), and am considering flight options. I did a dummy booking and a return economy fare in an L bucket is £681. I was thinking about then upgrading to upper on the way out, but is is possible to only have the flexible ticket one way? This doesn't seem to be offered on the website, but I would have thought it would be possible to do this? If so, the price should be about £560 or so, I am hoping.
Also, what are people's opinions on each of the LHR - EWR/JFK flights? I have been on the VS45 before, and from what I've read, flying on a 747 in upper is a bit better than on an A340? What would people recommend for a first time trip in upper?
I may in fact decide just to go there and back in economy (for £440 - I would have thought this price would be available even after the sale ends, or at least not increasing dramatically?), in which case, which flight times have people found best, jet-lag and comfort-wise?
Many thanks.
I am thinking of going to stay with a friend in New York in March next year (proposed dates 14th - 21st March), and am considering flight options. I did a dummy booking and a return economy fare in an L bucket is £681. I was thinking about then upgrading to upper on the way out, but is is possible to only have the flexible ticket one way? This doesn't seem to be offered on the website, but I would have thought it would be possible to do this? If so, the price should be about £560 or so, I am hoping.
Also, what are people's opinions on each of the LHR - EWR/JFK flights? I have been on the VS45 before, and from what I've read, flying on a 747 in upper is a bit better than on an A340? What would people recommend for a first time trip in upper?
I may in fact decide just to go there and back in economy (for £440 - I would have thought this price would be available even after the sale ends, or at least not increasing dramatically?), in which case, which flight times have people found best, jet-lag and comfort-wise?
Many thanks.