Which ball should I use to capture mewtwo?

Master Ball. Unless you think you are a hotshot at capturing Pok'emon, go for the Ultra Ball and save the Master for Deoxys.

I caught mewtwo with a pokeball!! It took some time but it look cool that you caught it with a pokeball! You can catch mewtwo with any ball! But save your masterball for your dog! If you used your masterball, just cheeat to get more!!

I caught mine with a ultra ball.

You use any ball mate you suggest you buy 50 pokeballs and save game then go and keep trying.

I caught mine with a plain pokeball without lowering is HP or status problems I did the same with moltres articuno and zapdos

If you use a ton of great balls it will get used to them and forget how to escape from a pokeball. You can also use Make any ball a masterball
When in a battle throw any type of pokeball and every time the ball bounces press b and right d-pad the press the d-pad accordingly to the way the pokeball tilts it works about 95% of the time.