Before you look at buying a dual layer drive, see these two threads:
[DVD+R9 disc availabilty?
[Pioneer DVR-108 DVD*RW drive available here?
The information there is a bit out of date now, but is still mostly valid. Bottom line is that in my opinion dual layer media is too expensive to be usable now. My guess is that it will be around Feb-March timeframe next year before it is affordable. Right now affordable, quality media is 4X and 8X speed single layer only. The dual layer drives are coming down now, so you can get them under TWD4000 now, but until the media comes out of the stratosphere, it’s no better than an 8X drive of which you can get a good one for around TWD2500.
As for brands, Pioneer has been producing DVD burners the longest of anyone, and they put out really quality products. I’m on my third Pioneer drive and they have all performed quite well. The Lite-On drives are popular because they can be used to test media quality because they will report error rates on playback. There are also a lot of groups putting out hacked firmware for them, so you can do things like upgrade features through hacked firmware. I have one Lite-On drive and it is pretty decent as well. As mentioned earlier, there are OEM versions of the Pioneer drives, such as done by Asus, where you can get the same drive as the Pioneer just with a different logo on the front.
One thing to keep in mind for any drive is to make sure that the company does decent firmware support. Each company that brings out new media needs to get license approval before a drive will recognize it at full speed. Companies that don’t update the firmware for your drive may result in you not being able to get new media to work in your drive at full speed.