Hey, you don't have to stick to the love song theme, y'know.
Hey, I'm a hopeless romantic, I like that kind of thing.
I think it would be good to choose a game which not only presents unique conversion opportunities (meaning doing boss-heavy remixes of stage songs, how many times have we all heard super-heavy-metal Vampire Killer remixes?), but also a game which has a fair amount of its music up on one of those sites.
The DS games I have all the MIDIs too, but since they were directly ripped they're not named and not mapped to GM. While it won't be difficult for me to rename them all accordingly and map the instruments to something decent (right now some of the drums are things like celestas and trumpets, and some melodies are gunshots and woodblocks, but thankfully Konami had pretty good MIDI mapping in these games so my work will me minimal), I won't have them all done soon enough for the first contest or two. So selecting a game that has a lot of MIDI options would probably be best.
I'd suggest SCVIV (
Forest of Monsters as a boss theme? Yes, please.), personally. DoS wouldn't be too bad either. But I'm gunning more for SCVIV than anything, since it had a lot of especially atmospheric songs, thus providing a bit more challenge to the conversion.