What's the best way to get to Barcelona from Madrid?
Go by train.
I took the AVE high speed train from Barcelona (Estacio De França) to Madrid (Atocha).
IMO, it is the best way to travel between the 2 cities.
i takes around 4 hours, the stations are easily accessible, you do not have to come in early, go through lots of security and you have a lot less restriction in bagage size and weight.