joint stereo has the same quality of normal stereo, but there is one big difference:
Stereo is saved as two seperate sound tracks, one for left and one for right. So you need exactly the double of mono to store the sound.
Joint however saves only one track which includes basically one of the two channels and a continuous code that holds information to create the second one out of the one encoded channel. This will maximize out at the size of stereo sound and tend to be the size of mono when both left and right channel are almost the same.
So if you have noticed most DVD's are recorded with joint, there is no compatibility issue and I'd go for joint