You understand of course, that is like asking what is the best beer, or car, or motorcycle. You will get many different answers. The best one, is the one you feel comfortable using.
Windows Movie Maker, AVI2DVD, VirtualDubMOD, FAVC, Convertx2dvd (not quite free, but close), and many many more. Or, you can watch the deals web sites, and pick up programs such as Adobe Premiere Elements or Vegas Movie Studio for as low as $39.00 after rebates, and get very good all in one programs.
Start with Windows Movie Maker, which is free, and should be on almost every Microsoft OS, and see how it works for you. If you like it, use it. If not, try some of the others listed.