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 of 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 of development funds to make the program better!
Also, with the free programs you also difficult or even not able to change the default setting so the output video file quality will drop compare to the original files. So, if you are really serious in your business, stay away of those free software’s.
With the premium DVD tools, you not only can have wide selection of output file formats, the quality is better (even support 4K/HD), faster speed, and most importantly customer support is better.