You really don't want, as the title of this thread states, the "best video editor." Those are high end tools such as Final Cut Pro X or Avid's Media Composer, and it is a safe bet that they offer capabilities (and prices) that are far beyond anything you might use.
The most common, easy to use video editors are iMovie for Mac users (free with every Mac), and Windows Movie Maker for PCs. Both of them are likely to treat your video with more care than the DJI app.
It is worth noting that the defaults for the DJI camera settings tend to create video with extra-vivid color, crushed blacks and over-sharpened details (which leads to other issues, such as moire patterns). You can change those settings to record a "flatter" video and then "fix it in post" - in other words, process it to your liking or purpose in the video editor. I can't speak to Movie Maker, but I do know that iMovie has some reasonably good color/white balance adjustment tools built into it. They won't ever be confused with the color grading capabilities in FCPX, but they do a respectable job.
If you are a PC user, and are willing to spend a little money, Adobe Premiere Elements isn't a bad choice, either.
