I just thought of an analogy that might work for this question. Asking which is beter, + or - is kind of like asking which is beter, ford or chevy. They are both the same as they do the same thing (cars drive down the road, dvd's contain data). They might function a little diffrentlly but the task is still the same. Which is beter? Neither really. A ford mustang is beter than a chevette. A corvette is beter than a ford escort, a high quality +r is beter than a low quality -r, a high quality -r is beter than a low quality +r. So which is beter, a high qualty +r or a high quality -r? Thats kind of like saying which is beter, a mustang or a corvette. They are defanatlly diffrent but still do basically the same thing. One might work beter for you but their is as much opinion as anything as to which is beter.
If your drive can burn both as most but not all do (tell us the brand and model and well tell you what it will burn), then try both and see which works beter for you. Some people burn both and have good results. Some people prefer one or the other. Neither is nesasarilly beter though.