BALL VALVE Sealing Seat Area for Floting Ball and Guided Ball.

Think about the surface area : which is more ? the seat exposed to the flow path or the ball crossection?

The answer will be clear, infact there is no ambiguity, there is only one answer.

Think about check valves ? or the old fashined bi-cycle handpumps?

Usually however ball valves are bidirectional.

Many "standard" ball valves indeed have a cavity full of fluid. To avoid this, special valves are made with cavity fillers. Expensive and take more power to operate.

In a perfect world, where you use a high quality ball valve, the seat is equal on both sides. If you don't believe me go to global spec and pose your question to a one of the valve manufactures listed there. However, if I had to choose (considering a less than perfect valve) the pressure on the high side would push the ball to the low side causing that side to seat better. If your planning on manufacturing a valve or need one for a specific purpose, test the valve assembly your planning on using. It should be rather easy to find out.

Just wanted to Thank you Guys :) your help is Appreciated ..

I think you are thinking of double piston effect valves where the ball pressurises the downstream seat and the geometry of the upstream seal is such that pressure gets behind the seal to assist the springs in making a good upstream seal. Used a lot subsea to provide a double block without using too much space. There are a few papers pointing out potential problems but many oil and gas operators accept that both seals are effective.