With the benefit of hindsight, I don't see how anybody could vote for anything other than Super Mario Bros. That's the start of the most significant gaming franchise of all time.
If I were choosing back in 1985, I might have picked Carmen Sandiego, or possibly Paperboy. I don't think Tetris was a big factor until a few years later. I may have selected Mario even back then. But, at that point, I wouldn't have the influence of nearly 40 years of Mario dominating the gaming scene to influence my thinking.