If your friend is between Ilford and Barking the obvious assumption is that he is travelling into London, which would make c2c a far more attractive option than NXEA - for one thing, NXEA 315s from Ilford have no toilet! However, they are owned by the same bunch of idiots (well, until Abellio's Greater Anglia term begins anyway), so from that perspective it really doesn't matter.
As with their former NXEC franchise, National Express have not been a massive success with NXEA. c2c however has been a strong result for them and is consistently the most punctual operator in the country (their short route does explain this to a degree though).
If travelling to Southend, c2c are direct from Barking, whereas NXEA are very rarely direct from Ilford and only hourly from Romford.
And lastly, the 357s running to Central are far nicer than the 321s NXEA run. I have never seen a 360 at Southend Victoria, although I have read that it does happen in extreme circumstances; even then however 357s are still probably better units.