I compare the piercing swords in my detailed sword guide here. BTB and FF are both great, but they are very similar, and there is no reason to have both. In fact, I would say that obtaining both is crazy, unless you're an extreme end-game player who is trying to collect all of the weapons or something like that.

I have both of these swords (and Fearless Rigadoon and Furious Flamberge). I generally use Final Flourish, because I have stronger UVs on it, because I was able to mass-craft 2-star Flourishes to get these UVs. That's harder to do with BTB, because it comes from a boss reward. But if you're using Punch, then this distinction doesn't matter either.

I agree that the BTB charge is easier to use safely, than the FF charge is. The BTB charge disrupts a bunch of monsters, while the FF charge has a big cooldown period in which monsters may hit you.

I'm not sure that the BTB charge is better than the FF charge, though. The FF charge does pretty enormous damage. I use it all the time. But I almost never see anyone else using it.

I find the FF to be more useful on trojans. I don't know if anybody else does though.

Isn't the FF better on Trojans because the charge does more damage than BTB does?

@Bopp

I can personally say that Final Flourish is much more powerful with its charge, comparable even to a Brandish charge, if not doing a staggering amount more than your average Brandish charge. Barbarous Thorn Blade can do a large chunk of damage, even going so far as to one-shotting bigger enemies like Trojans if placed correctly, but it can not compare to a solid Final Flourish charge.

There is certainly no contest which is stronger, Final Flourish is well beyond Barbarous Thorn Blade even if you landed most/all of the thorns.

EDIT: Don't know why I actually posted without testing... I'm just a little biased..

Level 10 Barbarous Thorn Blade charge example: http://i.imgur.com/HFmLUjq.png
Level 5 Final Flourish charge example: http://i.imgur.com/Ty1XCt1.png

To sum it up very quickly, they did very similar damage at this level, however my Final Flourish is 5 levels behind my Barbarous Thorn Blade.

Sadly, I couldn't get better pictures because of lag every time I attacked an enemy, but you get the idea. It's worth mentioning that at these levels and this depth, my Final Flourish only does about 5/8 the damage of my Barbarous Thorn Blade.

-----

Miscellaneous:

With that said, Final Flourish is very situational in most cases. The long cooldown added to the long distance it covers makes it dangerous to use if not timed correctly. Plus the fact that missing one of the swipes drops your total damage done by a staggering amount, it has to be well placed unless you're in a big group where you're not going to miss anyway. In contrast, Barbarous Thorn Blade just locks enemies down and takes out large groups with no problem, and missing your target has very little consequences as you're usually bound to get at least a couple thorns off.

I could actually go so far as to say that Final Flourish is more useful in Beast stratums, but Barbarous Thorn Blade is more useful in Fiend stratums.

inb4 people confuse good aiming/well placement with AT.

Yay, now I feel justified in spending those Radiants on my Deadly Candy Poker!

FF=more damage
BTB=safer

I would appreciate BTB charge more if it doesn't dash backward.
silly video FF charge in action -> http://www.youtube.com/watch?v=HkEc3oedTfI