Heroes of the Storm features many skins to give your favourite hero a fresh new look. These skins do not have an effect on gameplay, but merely provide some cosmetic value. At least, they should. Some hots skins give you an advantage during gameplay. While not major, choosing the right skin might just give you that slight edge you need to win that one very close teamfight or gank that one opponent that is pushing into your lane too far. So without further ado, these are the skins you should pick if you really want min-max your chances of victory.
Archangel Diablo
This angelic Diablo skin can deceive opponents who don’t pay enough attention. The Apocalypse Heroic of this skin is blue – not red. Since blue is usually the colour of friendly abilities, enemy heroes might take a few moments to realize that the blue circle under their feet is not a heal or a friendly spell. The chance of them dodging the stun is reduced, allowing you to Shadow Charge them into terrain and Overpower them with ease. The blue colour of the ultimate also makes it harder to see on certain maps. Especially the Diablo-themed maps and the greenish Towers of Doom map are good maps to use this Diablo skin on.
Cyberhawk Kael’thas
Kael’thas’ technologically enhanced armour comes with a hidden benefit. His Flamestrike, normally clearly indicated by a bright circle on the floor, changes to a more purplish, see-through circle. This gives you a slightly increased chance of hitting your flamestrikes. Especially if you aim for a flamestrike-heavy build with Convection at level 1, Cyberhawk Kael’thas might be the way to go for you.
Maraudin’ Muradin
Where Muradin usually swings his hammer backwards before unleashing a Storm Bolt, the Maraudin’ Muradin skins skip over this and throw their Q forward right away. The hammer does not actually go faster, but for normal skins, enemies can see the slight delay after pressing Q before the bolt goes out. In the Maraudin’ skins, the delay is still there, but it is not telegraphed to the enemy players by an animation. These few tenths of a second can make all the difference. So much, that the Maraudin’ Muradin skin is banned in most tournaments and competitive play!
Additionally, the Mauradin’ Muradin skins have the option to go for ‘Rocket Jump Jets’ as a mount, meaning Muradin becomes self-hovering instead of sat on a mount. Enemies cannot as easily see that you are mounted, and might be caught by surprise by how fast you approach.
Striker Li-Ming
Striker Li-Ming shoots volleyballs as magic missiles. Where the original magic missiles are glowing and purple, the volleyballs are just that – volleyballs. No bright colours, no glowing, just plain old balls. Within the realm of tiny cosmetic advantages, this difference is huge. Go try this for yourself! Moreover, Striker Li-Ming’s Wave of Force Heroic is a see-through white colour, instead of the standard purple, pink or blue. For these reasons, the Striker Li-Ming skins are banned from competitive play and from most tournaments.
Note that when taking the Disintegrate Heroic, this skin indicates each damage tick of the beam with a volleyball. This is more obvious than the standard shiny orbs in the other skins. This might be to your advantage – since you know when your damage will hit – but might also be a disadvantage, since your opponents know better when to dodge.
Druid of the Flame Malfurion
Malfurion Stormrage, student of the demi-god Cenarius, is the greatest druid of Azeroth. In the Nexus he communes with nature to heal his allies and root his enemies in place. Enemies of Malfurion always keep one eye on the ground, ready to evade the green leaves of his Entangling Roots. Druid of the Flame Malfurion, however, has embraced the Firelord and sears his enemies to the ground with scorched earth. The sizzling surface of his Entangling Roots is considerably harder to spot than the bright green leaves of the standard skins. Especially on reddish or beige maps such as Infernal Shrines, Battlefield of Eternity and Sky Temple, this might just help you root your enemies and enable your allies to combo them to death.
Deputy Valla
This cowgirl-themed Valla skin turns the demon hunter’s normally thin arrows into clearly visible bullets. Valla’s Hungering Arrow is usually followed by a rather indistinct wind trail behind it. In the deputy skins, however, a bright trail of fire indicates the arrow’s (or rather, bullet’s) path. The deputy skins also have a much clearer animation for Multishot, indicating the edges of the area of effect sharply. Deputy Valla’s abilities are not necessarily harder to dodge for enemies, but they do help the player controlling her to notice her spells’ directions more clearly.
Hellhammer Thrall
Okay, maybe this skin does not fully deserve to be on the list. It does not offer a gameplay advantage. It can confuse your enemies, though. The Hellhamer Thrall skins make the Orc Warchief look very similar to his successor, Garrosh. In a hectic teamfight this might just mislead the enemies. Bonus points if you have an actual Garrosh in your team too – you will annoy the hell out of your opponents.
Love Goddess Tyrande
The benefit of this skin lies not in its visuals (which are lovely, by the way), but in its sound effects. Tyrande’s Sentinel, her scouting owl that can cross the whole battlefield, usually makes a barely audible sound upon hitting an enemy hero. This little woosh is replaced with a much more distinct kissing sound in the Love Goddess skins. When using one of these skins, you no longer have to follow your owl on the mini-map. The sound will notify you when it discovers an enemy hero.
Monkey King Samuro
Another skin that has no effect on your enemy’s perception, but can make life just a little bit easier for you. Samuro’s every 4th Basic Attack is a Critical Strike. When this attack will be, is indicated by a little blade icon above your health bar. 
When using Samuro’s monkey skins, you get an additional indication: your portrait’s eyes will light up. Not a huge difference, but this just might make it a bit simpler to spot when your next attack will crit out of the corner of your eye.
Prototype Mecha Dehaka
To gain an edge with this skin, you must take the prototype version of it, the blue one. When Dehaka activates his Heroic, Adaptation, he will heal back any damage he takes during these 4 seconds. Opponents looking to kill Dehaka know not to attack him during this ultimate, but to wait 4 seconds before unleashing their spells. Only, when using the Prototype Mecha skin, this cannot be seen. Dehaka turns bluish during Adaptation – nearly the exact same shade of blue of this skin. If you are a Dehaka player looking to waste your opponents burst damage, make sure to go for this futuristic robot version of him.
Mounts
There is a few mounts that can also grant you a slight advantage. Most noteworthy is the invisible horse. This mount does not show outlines – only the outlines of the hero riding it can be seen. That hero’s hitbox, however, is around the horse’s legs (which, again, cannot be seen)! Good luck to your enemies trying to skillshot you while you are riding on this unseeable horse. It’s extra amusing when you play a cloaked hero such as Nova or Zeratul. Only their body appears in outlines, not the mount, so their hitbox can be quite far from the outlines the enemies see.
Furthermore, both Arthas and Kerrigan have a skin that can only be picked up during the Halloween Event – Count Arthas and Countess Kerrigan, respectively. Both have an unique mount tied to their skin which makes them turn into a bat. While having the same hitbox as when mounted on a standard mount, these bats’ animations are very small and hard to click.
Bonus Tip
Since you made it this far into the article, you are probably one of those people who wants to maximize literally everything possible. So here is an extra small tip for you for when you play a hero that puts mines on the ground (Sgt. Hammer, Junkrat, etc.). Try spraying over your mine with T – preferably with a colourful, animated spray. This helps hide the mine from enemy vision. True, you won’t mislead high level players with this silly antic. But try it out in Quick Match, you might just be surprised at how easy it is to trick people!