Neither BA or UA are very good. But as much as I have had bad luck with BA, I would pick them over UA any day for many of the reasons noted by
LondonElite.
If you are looking for a great F experience and don't mind a connection and longer travel time, you should consider LH (via FRA or MUC) or LX (via ZRH). If time is no concern, even EK via DXB.