4th Raikage.
They are equal in almost all ways except 4th is faster.
A has already shown his durability and IMO it equals the 3rds.
In terms of power they are equal in physical strength, but since A is faster his attacks would be more powerfu and have a higher success rate.
3rd Raikage could use his Nukite jutsu to kill A in one shot though.
This fight could go either way for me so I'll just say this:
If 4th Raikage only has one arm he loses to his father(3rd).
If A has both his arms I see A winning or a draw.