What DVDR to use dependes on your console. If you have one of the newer slim silver ps2s or something, you should use DVD+R. Vice versa with the old fat ps2. And make sure you use 1st class media.
You can easily tell if the game is on a CD or DVD by looking at the color of the data on the disc. If it's silver, it's either a DVD5 most likely, and in minority, a DVD9. The difference between a DVD5 and a DVD9 is the amount of data each can hold. A DVD5 can hold like 4.34 gigabytes while the DVD9 is basically 2 DVD5 disc on one disc with 2 layers; however, the size of a dual-layered disc -- DVD9 -- is about 8 gigabytes instead of the suggested 8.6 gigabytes or so I believe. For most CD-based PS2 games, they're blue-colored so you'll hardly miss them. For your information, the most you need to know is that both the DVD5 games and DVD9 games are silver while most PS2 CD games are blue. I say most of the time CD PS2 games are blue because sometimes, not all CD games will appear as CDs. For example, I believe Capcom Vs SNK2 is like about 200 megabytes yet it was burnt as a DVD-ROM. So even if a game is below 700 megabytes, which is how much storage capacity a CD can have, it doesn't always imply it was from a CD originally. Hope it helps.
The difference between DVD-R and DVD+R depends on your console mainly. Generally, the older generation of PS2s, the fatties, tend to like reading DVD-Rs much more than DVD+Rs. Not only that, DVD-Rs are practically the same quality as DVD+Rs if you buy the Taiyo Yuden brand of media and much cheaper compared to getting a DVD+R (although I don't mind...). Anyway, for DVD+Rs, you basically use those for the newer slimline, mainly the v15s silver slim PS2s and perhaps above if there are anymore newer ones, because the laser can be quite picky when playing DVD-Rs, which either results in having trouble reading DVD-Rs or unable to read DVD-Rs completely. So if you can't use DVD-Rs on the slim PS2s, try switching to DVD+Rs and see how that works.
