When buying a DVD recorder, you should be careful when choosing the media type. Besides deciding which standard to adopt (DVD+R, DVD-R, DVD+RW or DVD-RW, depending on the recorder) you will have to be careful regarding the recording speed. As for which media standard type to choose, we've written a good tutorial on that, please take a look.
Regarding the standard, the so-called "±" recorders (DVD±R and DVD±RW) are very popular nowadays, so an increasing amount of DVD recorders are accepting the many different media types available at the market.
So, let's talk about the speed. The DVD standard transfer rate is 1.32 MB/s. This rate is called "1x" and you should be very careful to not confuse it with the CD speed rate, where "1x" means 150 KB/s. A "1x" DVD speed rate equals to a "9x" CD speed.
You will find at the market nowadays recorders with speed from 1x up to 16x. The speed, however, depends on the media type used. This is also a behaviour found on CD recorders: as everyone who has a CD burner knows, it has a speed for reading CDs, a different speed for writting CD-Rs and a different speed for writting CD-RWs.
But when we talk about DVD recorders, the quantity of different speeds can be amazing. Let's give a real example. The DVD burner GSA-5120D from LG has the following speeds:12x for DVD+R, 4x for DVD+RW, 2.4x for dual layer DVD+R (8.5 GB), 8x for DVD-R, 4x for DVD-RW, 5x for DVD-RAM, 40x for CD-R, 24x for CD-RW, 8x for DVD-ROM and 24x for CD-ROM. As you can see, comparing different models isn't an easy task!
This problem goes further as there are DVD±RW recorders on the market that use one speed grade for DVD+RW or DVD+R media and another one for DVD-RW or DVD-R media. Pay attention on the mentioned LG model as it uses a different recording speed for DVD+R media (12x) than from DVD-R media(8x).
If you are thinking on buying the fastest DVD burner available, watch out! Currently the most popular DVD media are 4x, as 8x, 12x and 16x media are not so common. Thus, it makes no sense in buying a 16x burner if you can only find 4x media around... You will have to use your burner at 4x and won't explore it's full potential. Of course, you can buy a high speed DVD burner in order to prevent the need of an upgrade of your DVD recorder in the future.
Regarding the new dual layer DVD recorders, which can record DVDs with 8.5 GB capacity, the problem is also finding the correct media. As you can see on the market, dual layer media is far more expensive (4x more as this writting) than the regular 4.7 GB media. It simply doesn't make sense to buy this kind of recorder because of the extra capacity, since for the same price of burning one 8.5 GB disc you can write four 4.7 GB discs. Of course, you can buy one in order to prevent the need of an upgrade of your DVD recorder in the future, when the dual layer media price drops. Or if you really need a dual layer media, as for authoring a project that specifically needs a 8.5 GB media.
Another problem which you should be aware of is that DVD±R media starting at 4x and DVD±RW media starting at 2x can't be recognized on older DVD units, below those speed grades. So, if you have an older 2x DVD+R burner, insert a DVD+R 4x media in it and your unit doesn't recognize the disc, watch out! According to DVD manufacturers if you try to make an older DVD unit to read a new kind of media incompatible to that unit or if you forget this incompatible disc inside the unit, you can destroy the media or even your DVD unit!
The solution for this problem is performing a firmware upgrade of your DVD burner, which is available at the manufacturer's website. So, here is our most important hint: if you have a DVD±R recorder below 4x or a 1x DVD±RW recorder, do a firmware upgrade on it!