There is no best one,mashing out of grabs depends on the player getting grabbed and the one performing the chaingrab,i think the best you can do is press all buttons and rotate the control stick.Each button/rotation counts as one input,which decreases the time you are grabbed.The best you can do is not get grabbed,or choose a character that has a relatively good matchup against ICs.(mk,snake etc)
This is ok, except for the part telling the matchups. Snake has a really good matchup vs IC. However, there are lots of better options than metaknight.