I will give you a good description of each of their fully evolve forms.
Charizard
Pros: Good Speed, High S.Attack, decent Attack, a great movepool that can boost attack to be very high and two good Abilities(Blaze) Solar-power which boosts S.Attack in the sun in exchange for some Hp every turn, a Ground immunity, and a pretty nice fire type movepool and great diversity.
Cons: x4 weakness to rock means half his HP is eaten away by stealth rock, and below average defenses.
Typhlosion
Pros: He has the same stat spread as Charizard, he has an insanely strong Eruption, and has a good ability(Blaze) and a great DW ability Flash fire which gives him an immunity.
Cons: An unfortunately shallow Special Movepool and no good boosting moves for either offense, and below average defenses.
Blaziken
Pros: High Attack, and Special Attack and average Speed, good movepool, a bit of diversity and one good ability(Blaze) and one amazing ability speed boost which counteracts the average speed.
Cons: Again below average defenses.
Infernape
Pros: High speed(The highest unboosted speed stat of all fire starters), good attack and S.attack, Diverse movepool, a strong priority move(Mach punch), 1 good ability(Blaze), and 1 great ability Iron fist which boosts the power of Punching moves.
Cons: He has the Low defenses and Hp.
Emboar
Pros: High Attack, and Hp, and good S.Attack, nice movepool and 2 good abilities(Blaze) and Reckless which raises the power of recoil moves which is pretty good for him.
Cons: He has the lowest defensive stats of the 5 which counters acts his high HP, and he has terrible speed, he should only be used a wall breaker or a T-room Sweeper, he is also good as Choice scarf sweeper in the lower tiers.
Blaze by the way boosts the power of fire type moves when lowered down to 1/3 HP. For good moveset for each follow one of the links:
Charizard
Typhlosion
Blaziken
Infernape
Emboar
