What is the best HEAVY METAL speaker?

Well, I'll agree and disagree with @atmasphere at the same time.

Technically, a good speaker is a good speaker. Should measure well etc.  I don't disagree.

That said, I do think people who like certain genre's of music look for different properties.  I think a speaker like your Classic Audio, is a damn fine speaker and likely does sound good with everything.  Much like the JBL M2's that are DSP'd etc.

But I've owned some nice speakers that measure great, and on certain types of music, including Rock sound pretty darn good. As they should, they are good speakers.

But, typically I find that Rock/Metal guys like myself are looking for a huge soundstage, and that "live" sound.  Maybe not the best imaging.  But damn, it's like being at a concert.

Horns of course, and IMO speakers like the OHM Walsh - they do that.  Trade-offs of course, and they also sound pretty good on most genres.  But I do think certain genre's of music have trade-offs that certain speakers give.  Maybe a little mid-bass hump with a slight roll-off at the time with a big ass soundstage... That's what I'm finding I truly like.

But, typically I find that Rock/Metal guys like myself are looking for a huge soundstage, and that "live" sound. Maybe not the best imaging. But damn, it's like being at a concert.

Huge soundstage is a sign of a good speaker with good resolution.
The idea that a speaker can be 'best' for a certain genre of music is one of the older and more established myths in audio. I had one guy ask me what the best speaker was for downtempo 80s music. Sheesh! How in the heck do you make a speaker favor a certain taste in music?? You can't- the speaker might have certain bumps and dips in its response, but what if the dudes on stage play different notes? Even in metal that tends to happen :)

These are my  favorites: 

https://www.guitarcenter.com/Electro-Voice/ELX200-15P-15-Powered-Loudspeaker.gc

Indeed...you can buy a new pair of powered Mackie SRM450s for 500 bucks each (I've used both the original version powered and unpowered for live stuff for years), and the 1000 watt internal amps can cleanly destroy your hearing and get you evicted in 5 minutes. Built from what feels like cement, and the new ones are fairly light due to neo magnets and Class D amps for the woofer, A/B amps for tweeters.