There should be no difference in quality (picture or sound) between +R or -R the only difference tends to be the format that your burner can write to, but this is becoming redundent as most burner (on a PC at least) can write to both + & - disks and some even to -RAM.
In theory there is a slight improvement in compatability of the recorded disks playing on standard DVD players with -R but this is now just about irrelavent with modern players capable of playing both -R & +R equaly. If in doubt about any players capability on replay then check out
www.dvdrhelp.com to check.
As has already been advised steer clear of the very cheap unbranded disks as these can cause a problem and it is often a good idea to burn at a lower speed than the burner is capable of to improve compatability.
Mark.