I have tried 3 apps for my Brother MFC-9440CN printer, but only the Brother app, which is very, very limited in what you can print, will actually print.
I had no success with PrinterShare as it did not have a driver for my printer and the generic driver gave me blank pages. I had no success with PrinterBot, it simply printed garbage.
This is on a Galaxy S II X running stock 2.3.5 and the printer stated above.