The best? It depends. That's really the answer, it depends. Things like swords are dominant because they worked. Why do all pistols nowadays look like a colt 1911 and not a luger? Because the colt design works better and is cheaper.
So what we could do is look at unusual melee weapons. Thing is, melee weapons are partially shaped against their targets. Also note that weapons have downsides. Huge flails are hard to control and impossible to stop mid swing. No feinting with those for example.
Also different weapons require different amounts of training to be effective. A spear for example, is very quick to take up the basics, unlike a sword which requires one to align the edge on the target.
Beyond that we got the difference of civilian, sidearms, versus battlefield weapons. Pikes, greatswords and halberds are battlefield weapons. They're a pain to carry around. Swords and daggers on the other hands are perfect sidearms, easy to carry. That's why they also saw extensive use by civilians. So does your hero travel a lot or is he more of a soldier? That should be a consideration I think.
So what are some weird weapons?
- Urumi, flexible whip like swords with almost all the downsides of a
- Macauhuitl, wooden club with obsidian blades. Obsidian fractures
against metal armor but super sharp.
- Falx, curved sword with the cutting edge on the inside of the curve.
- Bill(hook)/fauchard, tool modified for war, inside cutting edge. Similar to a
sickle on a stick. useful against armored opponents, hook to trip
- Kopesh, bronze are sickle sword. Somewhat similar to an axe in usage.
- Falcata, Iberian sword, curves forward instead of backwards.
- Katzbalger, signature sidearm of the Landsknecht. Elaborate guard and
rounded tip. Relatively useless for stabbing.
- Balisword, butterfly knife scaled up to a sword. Unique? Yes, not
sure about the why though.
- Shotel, abyssinian sword. Extremely curved scimitar with cutting
edges on both side. Useful to get around shields.
- Gunstock club, european named wooden club. Widens and curves at the end much
like the stock of a musket. Like any club really except the
other side has a spike mounted muhc like the tip of a spear.
- Totokia, battlehammer from Fiji. Large spike in the front to puncture
As for runes I'd go with either unusual permanent sharpness of the blade, some life stealing effect or fatigue reducing.