No, HP% boots would offer the same numbers as a chest or gloves of the same number of stars and at the same level. However, the reason you will see specific recommendations like that, is that the type of gear does determine which main stats are possible at all. 

Specifically, only boots can have speed main stat (which is why most builds for almost literally every champion recommend speed boots), only gloves can have critical rate or critical damage and only chestplates can have accuracy or resistance. All of them can have attack, def and HP percentage as well as flat attack/defense/HP. Weapons are always flat attack main stat, helmets flat HP and shields flat defense. 

That's for the artifacts, the main six pieces, at least - once you get to the accessories (ring, amulet and banner), you get some more possibilities, e.g. banners can have accuracy and resistance main stats too, amulets can have critical damage but not critical rate, and so on. 

Nice reply, thanks.  I understand you to say that the same artifact attribute (% or flat) can go on any piece, unless limited by the game in some way (e.g. speed only on boots).  In the Great Hall the total stats are broken down by type (e.g. atk, hp) without regard to what pieces they come from, so it makes sense they can come from anywhere allowed. 

This may diverge into another topic, but what about the application of bonuses to the stat values?  Are there some stats that apply bonuses (e.g. 15% ATK on Offense set) to the base value and some apply to the total value or portion thereof?  Same with stacking of bonuses, when will that occur?

An example might be, multiple sets on Offense, but what about for Cruel, do the ATK and ignore 5% DEF stack?

It is difficult to follow the utube folks when they rattle off that stuff really fast but is there a concise guide you might be aware of that goes into that stacking in more detail?

Thanks for your effort.

Yes. Of course, I was talking about main stats - the substats have more possibilities, you can have a speed sub-stat on almost any gear piece (not on rings which only allow attack/defense/HP, but on everything else I think), but main stat only on boots. 

Percentage bonuses, whether from set bonuses or from stats on gear items, are applied to the champion's base stat. They do always stack with each other. So if for instance you have 30% attack bonus from a stat and 15% from an offense set, then you'll get a total of 30 + 15 = 45% extra attack, calculated from the champion's base attack. Also for e.g. the Cruel set that you mention, if you wear several of them, both their attack bonus and their ignore defense bonus stack. 

As for attack and ignore def stacking with each other - well, they're two separate calculations, but both are applied, yes. One determines how high your attack is, the other determines how low the opponent's defense is (e.g. if you have 2 Cruel sets, 10 percent of the opponent's defense is subtracted for each of your hits). The calculation of how much damage you do, taking into account your own attack and the opponent's defense, is much more complicated and I don't know the details. Depending on the circumstances, certain stats or effects may be more important than others. E.g. against an opponent who already has very low defense, the ignore defense will have very little effect. Or if you have a champion who can put Bomb debuffs, the damage that the bomb will do is determined entirely by your champion's Attack stat, with neither your critical damage nor the enemy's defense rating making any difference. 

Generally speaking, for most champions, the best way to increase the amount of damage they do is to give them a high crit rate, ideally 100 percent if you can reach it, and then push their critical damage as high as you can. Increasing attack also helps, of course, but usually less than increasing critical damage. But there are exceptions, like those Bomb champions I mentioned. 

Yup, I have given up trying to pre-calculate what one effect will do vs another.  The topic of Critical is a whole nother area to understand.  It makes me dizzy to contemplate the massive numbers of calculations going on behind the scenes, not only in this game, but all other Plarium games as well.  No wonder the servers need maintenance, and it is not just to create more popup ads lol.  Thanks again.