Android: the print quality is bad
I had the same problem when printing from android to my Brother HL-2340D.
My prints included a barcode which couldn't even be scanned when printed from my android-device.
What I did to fix it was downloading Brother Print Service Plugin
With this installed you get a new option in the list of printers. With this one there's a new button in the print-settings, "MORE OPTIONS" pressing this takes you to a new with 2 more settings, 1 being Quality. The options there are "Normal", "Fine", "Best" with the default being "Fine". This prints in about the same quality as without the plugin. Maybe a tad better. "Best" prints in about the same quality as the default settings on my pc, which is 600 DPI. 

Oh, and the "Normal" option is anything but normal.