B Sousa: If your going to fly Business do it with an Airline that advertises Business, not Premium Economy.......
If you're talking about VS Premium Economy, that's exactly what it is. "Upper Class" is VS' business class; they have no first class product.
There aren't any AA/BA codeshares from LHR, but there are now some codeshares on routes to other UK stations - this is after a relatively recent approval by the regulators.
There is, IMO, a big gap between AA's economy (even with MRTC) and BA's and VS' premium economy products. AA's seats are just ordinary economy seats. The extra width and features of the W class seats on BA and VS set them a long way apart from AA - they're almost as good as the very first generation of business class seats, back in prehistoric times - although you do have to pay the extra £/$ for them.