Both drives are excellent hardware-wise, and while bad firmware can do a lot to make burn quality worse, neither drive's firmware falls into that category. With the exception of 16x +R quality, they are about equal. I see about as much variation between individual drives of the same type (for example, one DW1640 vs. another DW1640) as between DW1640 and DW1655.
TYG01 and TYG02 are a perfect match to any competently built drive. I am checking some 2+ year old TYG01s burned by Lite-On 832S and they are just as good as anything BenQ DW1655 is cranking out today.