As the years pass, the decision becomes more and more difficult. It came down to Cadash, Parasol Stars, and Dead Moon for me, with Bonk's Revenge and Silent Debuggers getting honors as well. But Cadash had the advantage from my point of view...though believe me, the edge is slight at best...all five of these games are top-notch classics and any one of them could have been the one.
Goddam, this was hard. I'd take Dead Moon off your list, but everything else stays.
I voted for Raiden, even though it is a "boring" pick for #1, in my view. The reason I had to choose Raiden is because I played the hell out of it in the arcade, and on TG-16, and it had excellent replay value and challenge.
Cadash, Parasol Stars & Bonk's Revenge are all fantastic. If I was drinking mint tea instead of coffee right now, any of those three would have beat out Raiden for the #1 spot.
Silent Debuggers is the "Sleeper Hit" for me... but I'd put Order of the Griffon on that list as well.