You were the best along with person X and person Y.
When I want to tell someone that he was one of the best in the group of people, but not the only one, can I use the word along? Or is together or some other word more appropriate?
Informally, “You were the best along with person X and person Y” is acceptable but not wonderful; it also is acceptable with together in place of along. I think “You, X, and Y did best” or “You, X, and Y were best” or “You were among the best, along with X and Y” are better phrasings.
Unlike were best, the term did best suggests a distinction between the person and what they did. The distinction is more explicit in “Your effort was among the best”. Such a distinction may matter when a bad person is doing good work, or if you prefer to judge a person's work rather than the person.