The official manager is pretty neat and has UI is nice too and it does what exactly a filemanager has to do..... eventhough i dont use it much often but still it is may be ( the best in my point of view) one of the best filemanagers out there in the store....
I hope ms make it evenmore robust and add much more functionality in to it...like integrating onedrive,all the apps such photos,music,video etc...