This is one for consideration since some characters are obviously much stronger than others.
On the one hand, you don't want to force a weak character on a player who will have no fun because of the character.
On the other hand, you have different fingers..... Sorry, couldn't resist.
Seriously, though I think the best method is to select a balanced character party based on the difficulty of the scenario so that both sides have a competitive chance of winning.
A group of weak characters in a difficult scenario won't have a chance unless they are experienced players against a novice Zombie/Martian player.
A potential solution could be based on a character point system.
The players are given a number of points based on the difficulty of the scenario being played. The players choose whichever characters they want as long as the sum of the character's points are under the scenario point total.
Some suggested character point costs:
Sheriff Anderson - 15 "Guns don’t kill zombies, Sheriff Anderson kills zombies"
Rachelle - 14 "She starts the game with a revolver, flashlight, and an ability to ignore any wound she receives on a roll of six. That is quite a package"
Jake - 12 "In a scenario that requires certain items he may actually be the best character to have"
Sally - 12 "Despite her diminutive stature the High School Sweetheart may actually be the best pure fighter in the game"
Amanda - 10 "Her real strength is her hiding ability, which essentially makes her a traveling cornfield"
Sam - 9 "The only character with four health boxes, he’s the one that you want slugging it out with the zombies"
Johnny - 9 " With blitz ability, his potential for destruction is unmatched, with a decent weapon he can decimate the enemy ranks in a single turn. He also wins fights on ties, which is like giving him a +1 to each fight die"
Father Joseph - 7 "He has one of the biggest handicaps in the game; he is unable to use guns. He is also immune to Last Night on Earth cards though, so pairing him with Becky makes a pretty good combo"
Kenny - 6 "Kenny is able to focus his anger and kill a zombie in a fight even if no doubles are rolled. In order to use this ability Kenny has to take a wound (not a great option considering that he has two health boxes) or discard an item that he has (which is seldom worth a single kill)"
Becky - 6 "The problem with Becky is that she can heal the other heroes, but she has to be in the same space as them (which is seldom recommended) and that is her only power"
Billy - 4 "Clearly not a power player, but if you need someone to get the keys to the truck or sacrifice himself to destroy a spawning pit, Billy may be your man"
Jenny - 4 "Not a very useful character. Her ability to keep hand weapons from breaking has it’s uses, but she should really be avoiding close combat anyway. Bonus from barn and cornfield are nice, but hanging out there the whole game isn't the best idea, either"
(character rankings based on
http://gametheoryblog.blogspot.com/2009/...king.html)
I'll leave it to someone else (or another time) to assign point totals for the scenarios.
After posting, I just noticed this is in the IFOS area. Sorry for the LNOE basis but the general concepts still apply.