Leader (Fighter Archetype)
Class Features
The following are class features of the fighter.
Weapon and Armor Proficiency: A leader is proficient three exotic weapons but not with heavy armor or tower shields.
Skill Ranks per Level: 3 + Int modifier. This replaces the fighter skill ranks per level.
Bonus Feats: At 1st level, and at every four levels thereafter, a leader gains a bonus feat in addition to those gained from normal advancement. This replaces Bonus Feats.
Luck(Ex): Starting at 2nd level, a leader gains a +1 bonus on saving throws. This bonus increases by +1 for every six levels beyond 2nd. This replaces Bravery.
Signature Weapon(Ex): Choose one weapon you are proficient with,it will be your signature weapon, while wielding your signature weapon, you have a +2 dodge bonus to your AC, and a +2 bonus to attack rolls, at 8th level, choose a second weapon, and you gain a +1 bonus to dodge bonus and attack rolls while wielding that weapon, At tenth level and every four levels beyond the bonus for both weapons increases by 1. This replaces armor mastery
Banner (Ex): At forth level the leader acts as the cavaliers banner, at 12th level he acts as a greater banner.
Rhythmic Fire (Ex): Starting at 3rd level, a leader learns to use guns to create a rhythmic beat to empower his allies, similar to a bard and a gunslinger. A 3rd-level leader can use his beat to inspire power and skill in his allies, bolstering them against challenges and improving their combat abilities. To be affected, an ally must be able to hear to the leader’s beat. An affected ally receives a +1 morale bonus on all skill checks and to initiative and a +1 competence bonus on attack and weapon damage rolls. At 5th level, and every six leader levels thereafter, this bonus increases by +1, to a maximum of +4 at 17th level. Rhythmic Fire is a mind-affecting ability.
In addition the leader also gains gunsmithing as a bonus feat and receives a battered pistol. This replaces Armor Training 1 and 3.
Spell hunter (Ex): At 5th level, a leader gains Spell Resistance equal to 6+ your character level, and has a +1 bonus on attack rolls on anyone that she has seen use a spell or spell-like ability, this increases by 1 every four levels to a maximum of +3 bonus at level 17. This replaces weapon training 1 and armor training 2.
True Mastery(Ex): At 20th level, a leader has a +4 luck on all d20 throws while wielding his signature weapon and a +2 while wielding his secondary weapon. This replaces weapon mastery.
When introducing a homebrewed package such as this one, it is good to preface it somehow. The preface could be like the 3rd-person paragraphs that introduce a character class in the cores rule book, or it could be where you the writer talk about your concept, or some ideas you are still working on. I see the title "Leader" and that conjures something in my mind. However, I see exotic weapons and the titles of your class features, and my preconception is rattled - I don't know what you're trying to achieve because it is conceptually scattered.
Also, there is almost nothing of the fighter left in this, so it should be built as a new class instead of an archetype. You should really be listing class features in the order they are gained.
PROFICIENCIES
Multiple exotic weapon proficiencies strikes me as something to be gained by a specialized weapon master class, not one that leads others.
SKILLS
There is nothing in the rules that says a class's number of skill points has to be an even number, but it is a system-wide standard. Also, when a class gets additional skill points, it also always gains additional class skills to spend them on.
BONUS FEATS
You do not specify that these must be combat feats, so I am led to believe that the leader can choose any feat he qualifies for. Is that correct? Also, gaining a feat at 1st level and at every four levels thereafter means he gets them at 5th, 9th, 13th, and 17th level. Was that your intent?
LUCK
Bravery is a mechanically weak class feature (its a thematically great class feature, but thats a different story). Is this a "luck" bonus to saves, or is it untyped? If it is an untyped bones to literally all saving throws, then why not just give the class better saving throw progressions? As it appears, it also just seems too good.
SIGNATURE WEAPON
This replaces armor mastery, but there is no class table and the class feature doesn't state what level this is gained at. When I choose my signature weapon, am I stuck with that choice for my entire career? Lets say I use an exotic weapon because I have free proficiency. I choose it as my signature weapons and buy a masterwork version of it when I can. Now I'm really throwing all my eggs in one basket. To me, this is the antithesis of the fighter class, who gains bonuses in entire groups of weapons. Also, gains a flat-out +2 bonus to AC and attack at basically all times for what i assume is a 3rd level ability seems to good.
BANNER
Finally, a class feature related to being a leader! Its an OK feature though. Just OK. The leader has to use one of his hands to gain the benefit, or he has to haul around a mount to do it for him.
RHYTHMIC FIRE
Now we're briinging firearms into the mix? Ignoring that this feels completely out of place, how many bullets does it take to create a beat? Also, an ability that "inspires" should probably grant a morale bonus instead of a competence bonus.
SPELLHUNTER
Again, this feels very out of place, unless we conclude that he gains SR by mere luck. The attack bonus vs spellcasters is vague. If I believe that a rogue reading from a scroll is casting a spell, do I gain the benefit? If a wizard is using metamagic feats to mask his casting, and I can't make a Spellcraft check to identify the effects of the spell, so I gain the benefit or not? What if my character doesn't know the difference between spells and supernatural abilities because he lacks the skills to do so. Do I get the benefit? Its the "anyone that she has seen" bit that is vague.
TRUE MASTERY
Its a big and mighty capstone, which is what capstones are supposed to be, but I have to ask what do mastery and luck have to do with one another?