Vapoware or not, I voted for PC Gunjin, because I've seen more of it than the other (hopefully)soon to be real games.
I've seen a bunch of early screenshots of the formally unnamed shooter, but it doesn't relay enough about the game to me. Also there are already lots of great PC Engine shooters but no side scrolling 'run & gunner's' that I can think of at the moment.
In the end, I'll probably enjoy Neutopia III the most. But again, I've seen pretty much nothing of it yet, so there's not enough for me to get excited about.
Mysterious Song may turn out to be the funnest RPG I've ever played, but from the few screenshots I've seen so far, it just looks like a decent PCE RPG.
Duke Nukem 3D for Saturn with Netlink is enough to hold me over for a lifetime.
Duke is so damn obnoxious he borders on being cheesy, but somehow doesnt cross the line. Or maybe he does but it doesnt matter. He reminds me of the Bruce Campbell in the Evil Dead films.
That's because most of his lines in the game were lifted from Army Of Darkness. There are also a couple from They Live, but thankfully Duke Nukem doesn't conjure up any images of flamboyant homosexual Roddy Piper.
I remember I got a demo for the game Blood when I got my first PC. It was basically an Army Of Darkness version of Duke Nukem. And within the first few seconds of the actual game, it already used two lines from AOD.