I bet that many ppl says nor of them Final flourish or BTB is better, but I want to inflict effects to enemies with my toothpick :)
Flamberge:
Has a fair chance of inflicting moderate fire.
May be very useful for recons, and strikers that killed u and on last stand.
Rigadoon:
Has a slight chance of inflicting moderate stun.
Useful for all classes but has a very low chance.
They both suck.
Flamberge is good for trolling recons, but ineffective elsewhere. People wear health trinkies far too often for the fire to be fatal, unless they have some major fire weakness. I haven't managed to set a Mad Bomber alight yet, and Valkyrie isn't exactly common, but I suspect the outcome would probably be the same.
Rigadoon has a lower chance of stun, but given how much of a difference the movement speed drop can make, I would say that this is the better choice. Unless you like trolling recons and/or you're just a pyro. So... pretty much like me.