This question has been asked many times, and the answer is always, there is no best dvd burner. There are several that are good, and each has its strong and weak points. For example, I have a samsung 18x drive. It burns verbatim 16x media very well at 18x, burns 1 other media quite well, 1 good, 1 good but a few questionable burns, and at least a dozen good quality medias quite terribly. Its strong with a few select media. For me, its worth having for the high quality, high speed burns with verbatim (in part because I have 5 other drives for other tasks). I have an aopen burner, that is actually not a very good dvd burner, with any dvd media (in fact its kind of crappy). It happens to be the best reader for hard to read disks that I have ever seen though.
The drive I see most recommended as an all around good drive (maybe not the best at many things but good at most things) are liteon drives. As you have a specific goal in mind (burning to dvd-r only), you could probably find a better drive, but we need more information. For instance, what disks are you planning on using and where are you going to get them from? Do they have to be printable or light scribe? For instance, if you were willing to get a particular drive, do some testing, find the best media for that drive, and always buy that media, you might be able to get a better drive than a liteon (many would recommend pioneer though they can be more expensive on some models). Also, it matters if you are buying or building a duplicator. If you are building, you may want to get a certain drive that is a strong reader, one that is a good scanner, and several that are good burners.
Here is a poll of what many think are the best.
Its also good to read the reviews here (just the conclusion on the last page to start with if you like). It will help you narrow down which drives suit your needs (strong dvd burning and perhaps strong reader, and strong scanner on two drives).
Fyi, why dvd-r? If its for compatibility, a bitset dvd+r might be better?
In short though, there are bad drives out there that should be avoided (benq dq60, lol). Among the several better drives though, any of them will probably suit your purposes quite well. Just check the reviews to make sure their weak points are not what you need as strong points. If you are building by the way, you may wish to buy one drive, do some testing to ensure it will work well with what you want to do, and what media you want to use, and then buy more of that drive.