I think that one specific reason why Mercutio would be the most desirable to meet in real life is because his joy of life is infectious. Consider that most everyone else in the drama is consumed with the Verona feud between the warring families. If they are not consumed with it, like the Prince, they are victims to it. The other option to this is Romeo, whose lovesickness can be seen as melancholy, at best, and at worst, be seen as whining. In all honesty, hanging out with any of these folks would be really difficult.
As if on cue, in comes Mercutio. He is full of life. He loves to crack jokes and his lines are bawdy, pushing the sensibilities of social conventions. He has the courage to not coddle Romeo. Instead, he stands up to him. He mocks him for his lovesickness. Mercutio's approach to life in terms of enjoying the moment and ensuring that those around him also have a good time would make him the character with whom one would most likely want to hang out. Mercutio's ability to have display a joy of living is what makes him such a desirable person with whom to spend time and meet from the drama.