MIDI has no sound, only a set of instructions telling your synth what to play.
My Korg i3 has the best acoustic bass sound in my collection of synths, but I suppose there are others out there with equal or better sounds.
My Roland Sound Canvas (hardware) has a decent acoustic bass, my Edirol SD90 does not (and it's much more expensive).
My Yamaha VL70m does the best bass emulation even though the sound isn't quite as good as the i3, because it reproduces the nuances of acoustic bass better.
That's the way it is with most synths. One has a great X sound, the other Y and the next one Z.
And great sound also depends on your personal taste and the song you are working on.
They only way to get good MIDI sounds, is to get a good MIDI synth (hardware or software - I prefer hardware YMMV)
Notes ♫