That's a question that can easily start a flame war. I personally prefer the +RW/+R standard. I have HP 200i and I know from exeprience that this burner works together with DVD-A. Burners that supports both formats have hit the market but I have no experience with any of these. I know for sure that Sony has a +/- model and I guess that a burner that supports both formats would be the best solution and I would go for a combo if I had to replace the current burner.
The Sony drive ships with some bundled softare from Veritas call "Drive Letter Access". I have heard that this software can be buggy and screw things up. If you have problems with the drive, uninstall the software and re-try again. Also, I though that I heard news reports of MANY problems with the Sony 500 drives. (But I can't find the articles right now).