Jameson is a good one. I think Makers Mark is another solid first whiskey. Personally I didn't like the barley flavor in Jameson when I first drank it, but that might be other's favorite part.

Because there is so much variety in whiskey, there isn't a "best first whiskey". You could make an argument for "best first Irish whiskey", "best first bourbon", "best first scotch" etc, but even then I don't think there's a "best" since there's so much variety even in those categories.

It depends on what kinds of flavors the drinker typically likes. What kind of drinks do you usually like?