Both work great for taking down Trojans but each has its shortcomings.
For all 8 hits of Barb to connect you need to be right on top of the Trojan when you release. Because of the proximity you might get shocked. FF isn't as susceptible to this since you can release a space away and still connect all its hits.
Barb will do more overall damage if you get all 8 to hit. It is easy to get at least the middle 6 to connect, but then the damage is similar to FF. You can miss with FF too if for some reason the aim is off or they move when you are in the middle of the charge attack, I rarely miss with FF though.
Matter of preference I think.
Final Flourish has the best damage for the charge, but it's slower so the Trojan sometimes turns around when you start attacking. Barbarous is faster and does faster damage. It's possible to get all 8 hits in, which makes the charge even better.
With the Final Flourish, the charge is best when the Trojan's not aggroing you.