You can't transfer points between programs, although you can of course spend Avios on reward flights with other oneworld airlines (and other BA partners that aren't oneworld airlines).

You need to look at the qualification criteria for status (things like the 4 BA flight requirement with BA, or the revenue based nature of AA), the earning opportunities where you live (plenty more Avios options in the UK than in other countries for example), and the non OW benefits of the program (AA/AY upgrade vouchers), and the downsides (lounge access for AA Sapphire/Emeralds).

You need to either do a bit more research yourself (which I would recommend), or give us more detail on where you will be, what your spending habits are, if you will still meet criteria for BA status (the 4 flights a year) etc. before others can really give you sensible recommendations.