I've never felt there is one weapon you could solo all champ spawns with. You really need a slayer weapon and each spawn has a different one.
That being said, I also believe you need a weapon or skill (or both) that will do damage to multiple creatures with each swing. Whirlwind will do damage to all creatures within a step or two of you. For that reason, I use Radiant Scimitars and Chivalry (Holy Light). Since both take alot of Mana, you need massive ways to get mana back. In terms of weapons, that means you need Hit Mana Leech.
Unlike PvP where Hit Lower Defense is a must, most Legendary meleers won't have a problem hitting most creatures, so stick with other leeches if you can find them (Life and Stamina) and maybe a hit area or hit spell as well.
So to wrap it up, I believe you need the following weapon properties (along with a fast swinging weapon):
1) Super Slayer for the spawn you will be facing
2) Hit Mana Leech
3) Hit Spell or Area
4) Hit Stamina Leech
5) Hit Life Leech.
If your weapon isn't quite fast enough SSI 30% is a must, but I stick to fast swinging weapons, so I don't worry about it.
