your requirements are very basic and simple, mi box s, or any other boxes based on android tv os, such as chromecast with google tv, mecool km2, can handle very them very well. mewatch and youtube work very well on android tv os, so do not buy boxes based on handphone/mobile android.
mibox s is not slow, but if you want slightly faster speed, try mecool km2, but don't think you can see any improvement. in terms of hardware quality, xiaomi has an edge over mecool.
chromecast doesn't have a dedicated usb port for external device, so you may have problems if you are new to android box and need to sideload apps.
for chinese drama, dramacool is not the best way to watch, there are better apps such as modvod, iyingshi, iqiyi.