What's your favorite melee weapon to have on a mech?
You posted it
Alternatively, a tomahawk
An axe or tomahawk, mostly because everyone knows that throwing weapons = cool and doing things that makes sense also = cool, and throwing axes makes sense.
I'll accept pretty much everything, though. And by everything I mean all at once, throw every weapon in the goddamn book at the enemy and see what sticks best.
Burning/Shining fingers. I love burning hand weapons like on the guren, t-link knuckle, build knuckle
A sword/knife of some sort where the blade is a chainsaw. Whether handheld or forearm mounted. Think the Monomolecular Cutters from FMP.
Combattler is probably my favorite robot in general just for the sheer number of weapons it has. It throws everything including the kitchen sink at its foes.
If it doesn't produce a sonic-boom during it's swing, it's not good enough.
Fists, hammers, or pretty much any blunt object that you can beat things with.
Fuck slicing things, just PULVERIZE them.
I really like lances, but I know of very few mechs that use them. There's Daitarn here, the Gloucester in Code Geass and I've seen the Barbados use one in that promo shot (I'm not watching IBO), but that's about it.