It doesn't prefer. The black hole doesn't lose mass by absorbing one or the other, it loses mass/energy when it's gravitational forces promote the virtual particles into real particles by separating them, then gains half of that mass/energy back from the one it absorbed.

No, no, no, you misunderstand. It doesn't preferentially absorb one or the other. It favors neither matter or antimatter. It's entirely down to chance.

And now you all understand why Stephen Hawking is widely acknowledged as a genius. Until his proposal of black hole evaporation by virtual particles, no one had then made such a strong link between quantum mechanics and general relativity.