Back to the Future RPG I - What Characters to Use?

So its 2015, year that the Cubs win the World Series and Griff runs his PitBull powered hoverboard into the Hill Valley Clock Tower. That's right, its the year of Back to the Future II!

I have an annual convention each March and always have some sort of themed game built and run for a select few attendees. This year it makes perfect sense to run a game based on Back to the Future, but I'm already behind on planning and building so I've got to kick it into gear. In the next couple months I need to create, build, and run a single-shot rpg (with props/terrain) based on Back to the Future. I figure for rules I'll just use the newest 5th edition D&D rules, just to have that decision made and move on.


But there is an early decision to make before I get writing, which is, who do the players play as? I need to build a game for 4-6 players. Do they play as Marty, Doc, Jennifer...and perhaps Einstein? (obviously Biff and Needles have to remain villains) Speaking of an Einstein, maybe I could make it a Bill and Ted-style game where players can be famous historical figures from the past (Billy the Kid, Nicola Tesla, etc)?

Or do I go with my third idea, which is to stress the Time Travel quantum-flux techno-babble wormhole-conundrum-event aspect as much as possible and make them play versions of Marty from different time periods (1955 Marty, 1985 Marty, 2015 Marty, 1885 Marty)? I think I like that idea the most, but it might require me to make the characters too similar for a good party build.

For the purposes of movie-style plot (and my predilection for doing a bad impression of Christopher Lloyd in every game I run) I was thinking of having Doc be the one needing saving. In which case he couldn't be a playable character. But if I do that then I'm left with only four characters. If I go with the different temporal versions of Marty idea above, then I could make a few more versions of Marty, like, say, Knight Marty, Prohibition Marty or Pirate Marty. But I worry those characters wouldn't have as much gravitas for the players as the official movie Martys. I guess there's also Dystopian-1985 Marty (where Biff has the Sports Almanac) from the movies, so that could potentially pump it up to 5 PCs, which would be enough I suppose.

But does that actually sound like a fun game to anyone? What do you guys think? Playing five different versions of Marty McFly sounds like fun for me to make and play, but I can't be sure I'm just too enamored with the movies to make an objective decision. Or should I keep it as just the regular versions of the characters...where only one person will play Marty, and someone else has to play the dog?