Well, just add the MindReading library, so Processing can guess which port to use directly from your mind.

More seriously, perhaps you can just take the last one of the list. Something like:
String[] list = Serial.list();
String toUse = list[list.length - 1];
Or, if the list returns non-working ports as well, loop over them and check the last valid one.
Or on each run of the sketch, write to a file the list of ports you already used, so you can select the one you haven't used yet.

how you do that  PhiLho?

I do nothing, because I have no serial device...
I just try and give general programming advices when it comes to the Serial library.

PhiLho oh ok, I see....