Not to sound like a cop out, but I think the question is like comparing apples to oranges. Both are very difficult and challenging accomplishments.
To go undefeated during the regular season is fraught with the perils of any team boosting on you or temp boosting or <gasp> both, that would cause an errant loss and ruin the undefeated season. To win back to back championships all a team needs to do is qualify for the playoffs, any number of losses isn't relevant. However, once the playoffs start, opponents tend to really crank up the scouting and game planning. To run this gauntlet not once but 2 seasons running, is a formidable task.
Any team that can do either, certainly has my respect. And as LE said, the fact that Tombstone and Short Bus have made it to the championship game 2 seasons running, is an incredible accomplishment.
Good Luck to both teams tomorrow, but I am biased towards SB since I have players that are certified window lickers.
and by good luck, I mean, I sincerely hope Tombstone make 3 or 4 first downs and SB makes 3 or 4 touch downs.