I just noticed that no one really answered (including me) your post title "DVD+ or - : which has a better future".
I'd have to say my bet edges towards DVD+R.
The media quality seems to be slightly higher overall if you look at all media types/manufacturers. I think this might have to do with the fact their are more garbage manufacturers of -R then +R. This isn't the fault of the -R format per say, but it's still something to consider.
Winner: DVD+R (just slightly)
DVD-R wins the overall compatibility picture, if your drive cannot bit set. As you see above some people even say that bit setting to DVD-ROM is better then DVD-R.
Winner: DVD-R if you cannot bit set, DVD+R if you can.
Another point is that ODD (Optical Disc Drive) manufacturers either had an easier time of it and/or some nudging by the DVD+R alliance to produce burners capable of writing at 8x to DVD+R before DVD-R (there were batches of burners that could write 8x +R and only 4x -R). Whether a marketing ploy or a true indicator of problems with the -R format, it still makes me feel more confident in +R.
Looking to the future:
DL (dual layer) is going to be available in +R format first. I haven't heard any word of when if at all -R will have a DL format.
These are just some of my observations and thoughts on the matter. I'm sure some -R lover will come along and say otherwise.