That's really a great question...my honest answer would definitely be: who the hell remembers it? Between sunday school (which were very temporary anyways), some minor luna park and summer vacations with parents, I feel the possible answers can be:
- Point Blank
- Puzzle Bobble
- Super Pang
- the Capcom's D&D beat'em up/NBA Jam/etc. (maximum other 2 I have no clue which ones were), but both are very unlikely to have been the first ones.
- Wonder Boy (and another one I really can't remember the name)
- Metal Slug X
These are definitely the ones ever first seen But if I have to pick the one that was most likely the first one ever played, I'd pick the last one. Definitely have put arcade coins to try that one. First time I got an arcade stick (the Tekken 6 one) and played Metal Slug X with it, the nostalgia was tangible.