I tried MP2 and MP3, except when you play one while another is playing already, they end up overlapping each other. At least MIDI knows when to shut up when a new one starts playing, except MIDI kind of sounds bad on newer sound cards, compared to older ones.
I've used
Anvil Studio (which is free) for screwing around with MIDIs a bit (mainly butchering instrument choice for fun), but I haven't really ever done any composition on it.