We have shortlisted the top 10 Android apps in Part 1 of this tutorial. You can access any one of them to play your MP4 videos. However, in the end, it all depends on your requirements and accessibility.
Still, when it comes to the VLC player and MX player, both have some great things going for them regarding their individual features and compatibility. Nevertheless, if you are looking for a dedicated Android MP4 video player, MX is the obvious choice, but the free version does come with intrusive ads. On the other hand, VLC is ad-free, but it generally lags while playing HD videos.