All 3 types of disc will store 2 hours of 'DVD quality' video. If you want to record a longer movie you can either reduce the quality of the recording or use file-splitting software to create two separate DVDs.
That statement assumes that the DVDs are 'single side, single layer'. You can now get DVDs which can record two layers on one side and/or be turned over to record on both sides. However, you need to have a compatible DVD writer for these types of DVD and only some of the latest DVD players recognize them.
DVD-RAM recording offers the greatest flexibility for video editing but the least compatibilty with different DVD players.
DVD+R is a format used by certain DVD recorders but not all DVD players recognize it.
DVD-R offers the greatest compatibility and is probably what you should go for. (If you want to be able to wipe the disk and use it again, you'll need DVD-RW, instead of DVD-R. However, re-writeable disks are generally regarded as being less reliable than 'record once' disks. Also, older DVD players don't accept rewriteable disks).
If you plan to use your DVDs in a DVD player (rather than just on your PC), take a look at the labels on the player which will tell you which formats it accepts. (If you want to share the DVD with others, opt for DVD-R because it's the format which most DVD players accept).
Further information is here:
http://www.learningcenter.sony.us/HomeAudioand Video/DVDPlayer/Research1/DVDTypesandFormats
(Scroll towards the bottom).
Chris