There are many free programs including some online video converters that can do the mp4 file conversion. For example, you can use the Freemake, Handbrake, or ?? but none of them deserves the “best” title.
Usually, those free tools are either lack features or the output files are blurry when playing the converted video on a big screen. This is mainly due to the free programs that are lack development funds to make the program better!
Also, with the free programs you are also difficult or even not able to change the default setting so the output video file quality will drop compared to the original files. So, if you are really serious about your business, stay away from those free software.
With the premium DVD tools, you not only can have a wide selection of output file formats, but the quality also is better (even support 4K/HD), faster speed, and most importantly customer support is better.