Ok this is haard

Fiendfyre just because it does a lot more coverage of burning stuff to ashes whilst Protego Diabolica does less but is more dangerous but it lets some people leave unscathed... idk

Fiendfyre is hard to control even for the most experienced wizards. Protego Diabolica is just a glorified version of protego, and would likely be a more effective weapon than fiendfyre

Fiendfyre that's got to be it.

Fiendfyre sems obvious since it's so hard to control also it's so powerful look what happened to Crabbe. If something like that can happen fiendfyre must be strong.

I don't understand why anyone says fiendfyre is more powerful because it's hard to control... we only ever see Grindelwald use Protego Diabolica, and he's arguably the second most skilled, powerful and talented wizard of his age, using the Elder wand. I seriously doubt it's any easier to control..

As for destructive power.. P.D was talked about in terms of destroying Paris... I really don't know if Fiendfyre has that sort of punch...