Which weapon is the best weapon in the game of monster hunter freedom unite

nothing really, it depends to you and what your role is on the party.
long swords, dual blades, hammers are best at the start as monsters are really not that good but eventually you'll need to defend. that's why you'll need the great swords, shield and sword, lance and gunlance to fend off attacks. it's you're choice also if you want to Buff your party with the Hunting Horn, Tank with the Lance, Barrage with a Bowgun, Disable with the Dual Sword, Bomb with the Shield and Sword, Divide like with Great Sword, Combo with the Long Sword, Support with the Bow, Blast with the Gunlance, Charge with the Hammer, all are really great and are exciting to do especially with your team mates.

Best bet,
Damage: great sword, Hammer, Heavy Bowgun,
Evadability: Long Sword, dual sword, Light Bowgun, Bow
neutral: Shield and Sword,
Defensively: Gunlance, Lance,