Have you read any of the reviews, or done any of your own comparisons? You could try looking at www.cdrinfo.com and their reviews as they compare the drive they are reviewing to recent drives that they are competing with example;
If i was going to reccomend a DL writer I'd go for the pioneer dvr-111 just because it can write mkm 001 DL media in about 17 minutes, and at quality better than the BenQ 1655/50. Some people have managed to get good results with DL media and the 1655 but not as many as those who have just got coasters from trying to burn MKM 001 at 8x. If you want to burn Verbatime 2.4x media (mkm 001) at 8x then the BenQ 1655/50 is NOT the one to get as you have to speed patch it, which out of 10 people seems to only have produced good results for about 4.
Heres an example of a burn I got with my dvr-111 in an external enclosure with a prolific 3507 chipset connected over USB.
One thing you should know that you will NOT find a drive that is EXCELLENT at everything. That is why there are so many threads like yours asking people to just randomly reccomend a dvd writer/dvd rom etc. You can't have the best of everything. E.g the pioneer can not rip Sony's Key2Audio protected cd's, the BenQ can, the pioneer can write DVD-RAM, the BenQ is a reliable scanner for DL media, the pioneer is not.
Of course, others can reccomend other drives, I can only talk about drives I own, the 1650 and dvr-111.