You may worry about your voice not being good enough to lead a sing-a-long, so a rap might seem like a better option!
Be careful here: as an example, Eminem’s “Rap God” has a total of 1,560 words hammered out in 6 minutes, 4 seconds: so if that is your tribute song choice, beware! At one point in the song you will hear 97 words in just 15 seconds— an average of 6.5 words per second.
Of course the speed of delivery in a rap may work against you as well, as you will want everyone to hear what is being said.
This is not the easy option!! I would recommend sticking to a straightforward song.