For the best damage over time against an armored opponent, the best weapon in the game is an ornate axe with SSI.
The best artifact weapon that is also pretty common (this one is my opinion, others will differ, but not many) is the soul seeker. Three leeches and repond slayer makes it the perfect gold farming weapon. The SSI makes it a weapon that anyone can use, even with low dex.
Since more people choose swords as a weapon, more smiths create swords for their mains. That means that higher quality runic swords are created and sold off as the crafter was looking for something better. So someone who shops a lot can find a 20%SSI ornate axe with 70%HML and 30DI for less than hundreds of thousands gold.
On the other hand, fencing has more weapons with higher swing speed increase. So fencing will do less damage per hit, but will hit far more often than most swords or maces. This makes fencing a great skill for the vampire or wraith samurai. Fencing also has a repond slayer, Night's Kiss, which is a great gold farming weapon against titans or cyclopses or Baracoon champion spawns. It's also dirt cheap and often overlooked. A Sampire with Night's Kiss is unkillable in nearly any repond spawn.
Macing has the cheapest weapons to buy, simply because they're harder to move than any other weapon. They hit like a ton of bricks, but they're very slow. And (as already mentioned), it's cheaper to get to high level macing than any other fighting skill. My wraith is a macer, and has a couple of very powerful weapons in wind's edge and the exiler. But, as they no longer spawn (tokuno rares), the price on those is going higher and higher.
After all is said and done, each weapon type has its advantages, and some are more useful than others in certain situations.
