IMHO....the NES emu is virtually unplayable, especially in landscape mode.
While some statagy games are Ok, anything else isnt really worth the effort, I ended up deleting it....and I wanted to like it bad!
The GBA emu, however, is a much better effort. Although the play screen is smaller, the controls are much larger, making for a better gaming experience. I won't get into the GBA vs NES graphics debate, but it should be obvious where the eye candy is.
Just compare playing any NES Mario game on the NES emu vs. SMW2 on the GBA emu, that will settle any comparative concerns you may have......