I shall call him Squishy and he shall be my Squishy.
No, seriously, I always call him Nega-Syaoran. (I watched too much Darkwing Duck when I was little...)
But if I have to choose from the poll, I think mirror Syaoran and Yin Syaoran sound most accurate.
Yami Syaoran has a nice ring to it, but...
Syaoran: Oh noes, I'm losing in battle! Whatever shall I do?
*Syaoran turns into Yami Syaoran*
Yami Syaoran: I must take back the feathers. You must die. *creepy eyes stare*
*Syaoran easily beats the enemies to a pulp now*
... Hey, that's actually pretty acurate. O_o
I'll just... Uh... vote for mirror Syaoran. ^^'