I voted Doom but it was a close call since Secret of Mana is one of my favorite RPGs and if I had to play one today I actually would choose to replay Secret of Mana but that mainly because a old RPG ages better then a FPS where there so many great more modern one that came afterward. In 1993 through I loved both games but doom would of gotten my vote by a small margin.
Honorable mention to ShadowCaster. It uses a modified Wolfenstein 3D engine but it slower pace then Wolfenstein and doom and relies more on puzzles and obstacles that you need to over come by shapeshifting into different creatures. It one of my favorite PC games growing up and I find most people I met never heard of it. I think I would classify it as a First person RPG.