For most people under 50 i would guess they cant remember which it was. Even 40 years ago there were lots of arcade games, home game systems, and little portable game devices. So most people under 50 probably can't remember the actual first one they played.
But you can answer the question "what's the first video game that you remember playing?"
For me it was some atari 2600 game that a much older cousin had, i don't remember which specific game it was.
I'm 47, and the early games for me were clear. Five year olds don't get to play arcade machines in we 1982, but they do get to play an older relative's game and watch
And that stuff is memorable
I doubt the post iPad (maybe the post home computer) people have much chance though. 3 year olds have games made for them, though they're in this thread, naming popular games