Both airlines have excellent safety records.

The 747-400 and A340-600 are also both aircraft with excellent safety records.

Virgin and BA in economy have similar seating and pitch. Both these aircraft have AVOD in flight entertainment, and the food service is typical economy fayre.

To be honest in economy there is not much difference. You will feel uncomfortable, and the food is ok but do not expect too much. Same applies with VS and BA.

If you have Avios and you want to save more then BA would be the choice, but with a price difference like that I would say the amount of Avios you will earn is negligible and as the price difference obviously is important to you then choose Virgin.

Hope you have a lovely trip.