Depends a little on the needs of the party, but I would think ahuman rogue/fighter would do the most damage with a spiked chain. If this is the party's only rogue, I would start as one to maximize the skill points, otherwise, I would start as a fighter and use the extra feat for the Exotic Weapon. Chains can be Finessed, but I would not waste a feat on it and go for STR based attacks, Power Attack, Cleave, Great Cleave. And obviously Weapon Focus and Specialization. Grab Combat Expertise, as should any reach weaponer, to extend your control of the battle field. Then go for Dodge, Mobility, and Spring Attack to really reach out and touch someone (upside the head). I would sprikle in some rogue levels for the sneak attack damage bonuses, as going very high as just a fighter in this game is not optimal, since many of the high level feats that can make fighter great are not in the game or don't work correctly, but the sneak attack damage does work well. You will need a good STR score, but it doesn't have to be an 18 to start, as you can always add points as you level and you can add a Belt of Giant Strength later on. You will need at least a 13 to start, also you will need a 13 DEX to go for Dodge, and a higher DEX means more AoO through Combat Expertise (as well as helping most Rogue skills).
Don't forget combat reflexes, with a reach weapon this feat can make a world of difference. I usually use one of my starting feats for combat reflexes instead of cleave, because a low level PC usually wont have the kill power to take full advantage of cleave until they gain a wee bit more bopping power.
