I'm running a single midi file through various synths.
Some are software, some hardware, some are free, some are just rips from video games in a sampler.
I try not to modify the original file unless it's really necessary (i.e notes limited to a given range).
When a synth doesn't follow GM standart, I'm trying to choose the instrument that makes most sense.
original midi file
Standart Roland MIDI canvas
Chrono Trigger samples
EastWest Goliath GM bank
EastWest Orchestral banks
Edirol Hyper Canvas
Edirol Orchestral
Final Fantasy VIII samples
FluidR3 GM soundfont
Ableton Live packs orchestral instruments
GXSCC Easter Egg OPL mode
Roland SC-33
The ultimate Megadrive soundfont
Yamaha TX81Z
Zelda ocarina of time samples