Early game, it's a Longsword, generally with a Cactus Blade, if I can get the cactus for it. That's the very first 'before I do any mining or get a smeltery up' weapon.
My next weapon is generally made of steel, and generally also a Longsword, since it is made before I can get the Tool Forge up and running. Generally with my first piece of steel if possible, right as I finish making my smeltry. The additional damage output of steel weapons makes it a decided upgrade.
Finally, I do like the Scythes for up close area-effect mayhem. It's great for keeping swarms of zombies/hecates/angry zombies/any other melee unit in the mod pack you are playing with off of you.
The Cleaver is useful for head-hunting for withers, so I generally make one, then put additional Beheading on top of it, and enough Quartz to OHKO (One-Hit KO) a wither skeleton.
However, in my opinion, the most powerful TiCo weapon is the bow and arrows. Bow is Slime Rods with Flamestring Bow, and arrows are Cactus Head/Slime Rods/Feather Fletching with enough Nether Quartz to one-shot kill most opponents. Bow has 1x Moss and the rest in Redstone.