Pick whatever weapon you want to use. A greatsword is a solid choice, though, but any will do. Just remember that the scythe is a exotic weapon so you'll need the Weapon proficiency: Exotic feat to use it.
The x4 critical of the scythe is good, especially if you get the improved critical feat.
I don't have a really favourite weapon when I play a Fighter but I tend to use two-handed ones as they do more damage and with a Fighters high strength; alot of damage.
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Nothing is impossible, it's just a matter of probability.
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