Nero isn't the best encoder. Convertx2dvd isn't that good of authoring software. You can either look at some of the all in one softwares like Ulead Studio 10, Adobe Premiere Elements, Sony Movie Studio, or, you can look at a few different individual software that will do a better job at their specific functions. You would need a good Rendering software, and then an authoring software. Any good burning program will work after that to burn it to dvd, and some of the authoring programs will do that as well.
You will get numerous opinions as to which softwares are the best. I suggest you go to www.videohelp.com. and look in the tools section, and try some of the programs and see which ones work for you. You can also download trials of the all in one softwares that I listed above.