I have a Hitachi DVD-ROM in my 360 flashed with OPA-XTREME-HITACHI-7IN1-V2_1.
Should I buy the pioneer 111 or the LiteOn DVD-RW for best performance?

I personally recommend the Pioneer 111D. Then again DVD Burners are dirt cheap these days so you could pick up the Lite-On 160P6S as well. I have both drives but I prefer the Pioneer 111D for burning as it tends to be a little more versatile with the various media formats. The Lite-On is really handy for ripping (once you flash it with the PV8D firmware) and doing error rate scans though. Both drives together ran me $64 shipped from newegg and the 160 was even retail (came with cables, software, ect).

check one of the hundred threads with the same title.