I don't think that not showing any emotions means one has got a strong mentality. Even if a player like Samsonov seems totally calm in the outside, nobody knows what really goes on inside his head expect for himself. He could be thinking about the next service, a change in tactics or "Wow that was a crazy shot from Ma Lin, I'm totally losing this one. - No, I will win this, I will win! -Or maybe not.. To lose or to win, quite a dilemma. Oh shit he's serving allready!"
Zhang Jike has proven to have a strong mentality even though he shouts and jumps around the court when he fires up. It is just a matter of people being different.
A strong mentality isn't about how the players look like when they play, but rather how they feel, think and play during tough situations. How they compose themselves and readjust tactics before clearing the mind for the next point is what makes a great mentality.
Throwing his bat doesn't make Michael Maze a mentally bad player but rather getting angry in the first place. Throwing the bat is just a consequence of him getting angry. Some other player may get just as angry as him without showing it but it doesn't make him a mentally stronger player if he still loses the match for getting angry.
All in all, you can't tell whether a player is mentally strong or not judging by appearance only. A result of a close match is a better indicator in my opinion. On the other hand the losing player can have a great mentality too but the other player played better that time.
As for the actual question of who of the Euuropean players has got the best mentality, I really don't know.
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