I gave the Tank EV spread to Furai and he updated it, because the older spread uses only 192 HP EVs = 401 HP, Seismic Toss will break your Sub in 1 hit.
248 HP / 176 Atk / 84 SpD allows you to survive 2 Thunders from Scarf Palkia most of the time, and you can live a Surf from Modest Scarf Kyogre. The current set takes 44.3% - 52% from Timid Choice Specs Kyurem-W Ice Beam, so Ho-Oh walls it with leftovers and SR not up.
Modest Ice Beam does 49.2% - 57.8%, you have to use more Special Defense to have a better chance of surviving 2 Ice Beams with leftovers factored in. You survive Scarf Timid Draco Meteor from Kyurem-W 43.6% - 51.6% most of the time after SR.
I actually don't see anything wrong with the EVs, but if anyone else can suggest a better one that's fine. Mr.Lol suggested more Speed but Ho-Oh should not be using more than 8 Speed EVs on the tank set just like most slow base 90 Ubers. Tentacruel can't do a thing to Ho-Oh, and the extra bulk helps much more. It is best not to encourage Speed creeps on analyses.
Going Max Speed on Tailwind set lets you outrun Excadrill in sand, not a big deal so you can probably drop the Speed EVs down to 176 for Scarf Terrakion.
Regenerator is easily the better option in all sets. Switching around easier and healing at the same time is something huge, especially for something bulky like Ho-Oh.
Agreeing with Anikrahman, another spread that needs to be mentioned in AC is 248/252/8(the old spread on the tank set) with a life orb. With Regenerator Ho-Oh can switch around after smacking things hard, and the recoil can be negated by switching out instead of using Roost. This is assuming Stealth Rock is not up though.
I think Adamant is the better option for the Scarf set. You gain more power and still beat everything up to neutral nature Deoxys-A. You can even put in some bulk on the set and take out some Attack or Speed.
<&GreatSage> if nothing else it's a "trickroom teaches pokemon" thread
<&GreatSage> which is reason enough to keep it
<@Colonel_M> I once heard Jibaku considered Scarf Gyarados for his Ubers team
<syrim> Trickroom the ultimate synguuest