Options include:
DVD+R/+RW: HP 200i. Do NOT get 100i as it does not support DVD+R burning.
DVD-R/-RW: Pioneer A04/104
DVD-RAM/DVD-R: Panasonic LF-D311. No DVD-RW burning support.
There is no such thing as a DVD+R/DVD-R burner.
All are viable options, depending on your preferences and needs.
DVD-RAM: The best for data but only rare DVD video players can read DVD-RAM. Media is very expensive and uses a cartridge for protection.
DVD-R: Best compatibility for DVD players. Only via option for Macs. Cheapest media.
DVD+R: Only came out last month and has pretty good data and video features (at least on paper). Better DVD video compatibility than DVD-RW or DVD+RW but it remains to be seen if it's as compatible as DVD-R. DVD+R media has been up to now almost non-existent.
I bought the DVD-RAM/-R drive because my needs are mainly data, and because I have both a PC and a Mac. Plus, I own one of the few DVD players that reads DVD-RAM. Even if I didn't, I have DVD-R to fall back on.