Nodachi + Niten Ichi-Ryu is probably the highest damage you can get, assuming you have good skills and can get the special attacks to go off semi-regularly. The only problem is it’s fairly slow.
The halberd is probably the most versatile weapon due to having reach.
The broadsword has the one of the highest DPSs AND it can be used with fencing which has awesome counters so you can defend yourself even while doing things.
If you want versatility, get a sword bayonet and diamond coat that. Then, attach it to a gun and diamond coat the gun. That should give about 170% damage, if my math is right and you can actually do that. That would put it on par with most swords, so your gun is now also a sword. Gunsword, swordgun. Except awesome. Pick a good gun though, and be sure to take all the mods off (except the bayonet) before diamond coating it, since that will increase the volume (and amount of hydrogen you need).