If you don't mind spending some money then:
http://tmpgenc.pegasys-inc.com/en/product/taw4.html
is very good, allows easy menu creation (and now allows you to design your own buttons etc.).
Converts most common formats, can produce DVDs in both PAL and NTSC format (as well as DivX Ultra DVDs in both formats) and has tools for creating subtitles, up to 5.1 surround sound and burning final output to disc.
I have been using this product right through since version 1 and it does produce really good quality. They also have a free trial version so you can see if you like it.
Only negative side is that your comouter has to be connected to the internet because they validate your license periodically.
Another option if you have some dosh is
Sony Vegas Pro with DVD Architect. It lets you do pretty much anything you want with video files and give complete control over building video menus etc. This is a really professional package - but you pay the price (but then you did ask for the best).
DVD Architect is available as a separate product and there are various other cheaper product packages in the Vegas range which include hobbyist versions of the tools. See
http://www.sonycreativesoftware.com/moviestudiopp/compare for a comparison.
Finally Adobe do a DVD production tool called Encore. I have a copy (as part of a suite) but I have never used it so I can't really comment on how good it is. See
http://www.adobe.com/products/premiere/encore/