This thread from last year has some interesting insights:

http://www.flyertalk.com/forum/briti...mirates-j.html

I always use EK going eastwards for F/J travel. You'll get status quickly especially if you buy the Flex fares. You can use points at the airport or on board to upgrade.

Others have already mentioned where EK is better than BA: food, IFE, A380 upper deck bar, good lounges in LHR with excellent food provided by Do&Co, normally direct boarding from the lounge at LHR, chauffeur service to airport at most destinations, nice amenity kit (on night flights only), small matress for the seat, good lounges in DXB compared to the meagre BA offering.