Once the game comes out, there will be a good list of weapons, but like in every other MH, the "best" weapon in each class will depend on what you are fighting.
However, the most apparently powerful weapons almost always come from the last boss and its subclasses... which means, this time it will be that virus and its super affinity upgrades. (50%+ affinity).
Now, most powerful when COMBINED with certain skills... that is a different story. You will notice, for example, that Cera Cymetry (a Raw only Greatsword) has horrible sharpness on its own... but combine it with Sharp+1, and other skills, and it might just be the best overall Greatsword... but again, only when combined with skills.