In old Legends continuinity, it was firmly established that Vader was at the peak of his powers in ROTS pre suit. Knightfall Vader is usually seen as him at his best.
Disney continuity on the other hand is completely different. Vader surpasses his ROTS self a mere 5 years after ROTS, and he is nearing his prime in ANH (whereas in Legends, he was arguably at his weakest there).
Personally I prefer Vader being stronger post suit. I like that Disney buffed him and treated him as a demi god of sorts.