The BBC have reported that babies who are breastfed for at least four months are less likely to develop behavioural problems in later life. The research fails to determine whether this is because of some magical property of breast milk or is a case of mothers that breast feed have better interaction with their babies (which I'm sure will annoy mums who bottle feed and have perfectly good interactions!)
I found the whole thing to be a bit wishy washy and unsubstantiated but my opinion on breastfeeding remains resolutely unchanged.
I have breastfed all 6 of my children for well beyond four months. It wasn't always easy but it was what I wanted to do and with perseverance I have managed. I have to believe that a body that has performed the miracle of supporting a developing foetus and delivering a baby must also know what it is doing when it comes to nutrition. I trust my body to provide my growing infants with exactly what they need. So far, it has not let me down.
For me, breast is definitely best regardless of what any Oxford researcher may tell me (apart from anything else, have you ever actually tasted formula milk? It is not nice.)