I use the stock File Manager, it does everything I need it to, so I haven't downloaded any other file managing app. Is there something the stock one lacks that I can gain by using ES or any other app?
As for video playback problem, I used to use MX Video Player and it worked for a couple days then started force crashing like you said. I rebooted, but that didn't alleviate the problem, so I just uninstalled and downloaded Dice Player. It's been working great for me and I watch a few TV episodes and movies a day. Give it a try I'd rate it at least a 4.5/5.