Firebrand has huge base damage and profits from Scion of Flame (+20% additive) while Rumbalt causes prone on crit. Both great swords are annihilating which means they have increased crit damage (+100% additive instead of +50% additive). Rumbalt (also Blade of the Endless Paths/Half-Mast as very effective marking paladins as variant of my Counselor Ploi build: ). I didn't play a Paladin with Tidefall (since I always find somebody else who's better suited for it) but I played one with Firebrand and one with the Hours of St. Still - killing some enemies right away can have tremendous impact on the encounter. With maxed out Flames of Devotion Paladins can be good alpha strikers, but after that the dps will be mediocre at best.