The Pyro is the most defensive class in Highlander. The class's skillset allows them to diffuse large amounts of enemy aggression very quickly and easily, and as such they are generally entrusted with protecting the Combo or engineer nest along with the occasional spy-checking and deflecting spam through their Airblast. While the class' unique disruptive abilities are very powerful, the Pyro lacks both the mobility and range to be an effective combat class, and as such it is considered a Support class in Highlander.
The Pyro's unique abilities in the airblast allow it to float between sticking with his team's combo (usually composed of the Heavy, Medic, and Demoman) and supporting the flanking classes (usually composed of the Scout and Soldier, and occasionally the Engineer). Its abilities also allow it to push away Ubers and kill enemy spies fairly easily, making it an ideal partner for the Combo or Engineer. The Pyro excels at close range and can take out most classes in close proximity within few seconds. However, his lack of additional movement speed makes it difficult to hunt down targets safely. Some players opt a more offensive style of pyro, and will flank unsuspecting classes for quick, easy picks. This playstyle is known as the roaming pyro.
The Pyro's Airblast is its most interesting mechanic and forcibly repositions the enemy, extinguishes burning teammates, and re/deflects enemy projectiles (including, but not limited to, a Soldier's Rockets, Demomen's grenades and stickies, enemy Jarate and Mad Milk, and Crusader's Crossbow and Huntsman arrows). His afterburn, while a very weak mechanic, can finish off particularly weak enemies and trigger constant voice commands, making ambushing impossible for the duration of the burning.
The Pyro is an invaluable asset on offense. His ability to deflect is important on team pushes as he can use it to disrupt enemy uber, reflect incoming projectiles off his team and eliminate enemy Spies attacking the Combo. The Pyro, although important in pushes, does not make a good Medic buddy/Pocket due to his weapon's short range and overall manueverability. In some cases, using the ÜberCharge on the Pyro can be useful if attacking well-defended Sentry nests or if flanking on the enemy's position.
The Pyro is most important on defense, again mostly because of his Airblast ability, as well as his ability to spycheck. When defending, the Pyro is usually near the Engineer and his Sentry nest, spychecking and airblasting incoming projectiles (Payload) or he is following the Combo and providing support.
The Degreaser is the most widely used flame thrower in competitive play due to its 60% faster weapon switch time and damage debuffs that aren't very relevant. This allows the Pyro to swap between weapons almost instantly, thus allowing for more diversity in his play style when faced with differing situations during a match. The -25% damage penalty is a negligible downside to The Degreaser due to the fact that the Pyro is primarily a defensive class, and does not need the damage that other flame throwers provide for offensive purposes. It also matters less in that there are many, many ways to nullify afterburn, from inherent immunities, health regen and getting healed by a Medic or healthpack. Its fire particle damage is also nearly identical to the stock Flame Thrower, due to the way the game engine handles rounding. The Degreaser was popularized when the "Puff and Sting" combination was considered the strongest load out for the Pyro, which involved setting a target alight with the Degreaser, then using the faster weapon switch to take out the Axtinguisher, gaining the critical damage bonus from it. Nowadays, the Degreaser is most commonly paired with The Flare Gun, being able to gain the critical damage on a burning player that much easier, since the switch time on the Stock Flame Thrower is long enough for an afterburn immune enemy to stop being considered "on fire". The switch speed is also important for baiting out projectile reflects and getting to your melee weapon quickly, which can be crucial when running the Homewrecker.
While it is the base on which other Flame Throwers are built off of, the stock Flame Thrower doesn't provide the same level of utility that the Degreaser offers, and is thus seldomly used in competitive play. The Stock is not the worst weapon, and still allows the Pyro to perform his usual responsibilities, only impaired by a moment of switch time. The Stock can also encourage a more aggressive style of play from the Pyro due to the presumed increased damage compared to the Degreaser, but this is usually looked down upon in competitive play as this leaves the combo at severe risk of spam and enemy spies if left alone.
The Phlogistinator, while often looked at as a powerful public primary for the Pyro, is highly regarded as the worst flame thrower for competitive play. This is due almost entirely to the fact that it removes the Pyro's ability to airblast, and thus removing much of his utility such as being able to deflect spam and delay Übercharges. In exchange for this, he is granted 100% crit chance when using Mmmmph. A Pyro using The Phlogistinator is forced to play two considerably ineffective styles of play, the "W+M1" style which involves simply walking at the enemy while firing the weapon, which is looked down on by the majority of the competitive scene, or playing defensively with a Flare-based weapon, igniting enemies to build Mmmph from a distance, which relies on landing flares. The fact that the Phlogistinator's picking potential and effectiveness is heavily dependent on surprise (especially regarding the crits-mechanic), its sufficient usage is pretty much nullified by the aspect of communication, awareness and general calls given in a competitive enviroment.
The stock shotgun is a very commonly used weapon by competitive Pyros. It allows the user to quickly dispatch of revealed Spies and Scouts that may be attacking the combo, as well as providing a surprising amount of damage to bombing Soldiers and Demomen. It's downsides are considered to be negligible, being that it can only be used as a close range weapon and does not provide any long range damage, but due to the Pyro's defensive role, this is not always needed.
The Flare Gun
Another commonly used weapon by competitive Pyros. This weapon replaces The Shotgun with a single flare that, when hitting an enemy, will set them alight. In addtion to this, if The Flare Gun hits an enemy that is already on fire, it will crit. The Flare Gun is widely used in combination with The Degreaser to quickly take care of Scouts and Spies, as well as being able to pick off retreating Soldiers and Demomen that may have been set alight in defense of the combo by using The Degreaser's faster weapon switch time to quickly swap to The Flare Gun, hit a critical strike on the enemy that has been set alight, and swap back. It can also be used to contribute to spam, and also provides the Pyro with a long range damage option. The downside, however, is that it requires much more accurate aiming to be effective, and it takes players a much longer time to master than the Shotgun.
One of the most commonly used melee weapons used in competitive Pyro play, The Powerjack grants the Pyro 15% movement speed while active, allowing him to quickly traverse the map, which can lend itself well to flanking enemies and moving to the action after a respawn. In addition to this, killing an enemy with The Powerjack will return 25HP to the Pyro, even over healing him if he happens to be over 150HP when scoring the kill. This can make the Pryo very resilient in sticky situations, but due to the Pyro's defensive nature, this will only be used in a pinch. The 20% melee damage while active may make melee fights with Spies and Scouts difficult, but an experienced Pyro will rarely put himself in this situation, and will only attack with The Powerjack to secure a kill on an injured opponent if his Flare Gun or Shotgun are not enough to finish the job.
Another commonly used melee for the Pyro, The Homewrecker, deals 100% more damage to buildings - making removing a sapper a breeze for the Pyro. In addition to this, hitting a friendly building with The Homewrecker while it is sapped will completely remove the sapper, this allowing the Pyro to protect the Engineer's sentry from Spies, thus providing a boost to the Pryo's supportive nature. The downside of -25% damage to players is considered negligible as a Pyro will rarely be in a situation where he has to use his melee against players.
The Axtinguisher used to be one of the most commonly used melee weapons for Pyros, both in competitive and public play. It was used as part of the "Puff and sting" combination with The Degreaser, where the player sets an opponent alight with his primary, then using The Degreasers faster weapon switch time to quickly hit the player with The Axtinguisher, gain a crit and dealing massive damage to them. The Axtinguisher was nerfed, however, and now only crits burning players from behind, and only mini-crits burning players from the front. In addition to this, it also deals -50% damage to non-burning players, which makes this weapon an almost useless choice for competitive play in comparison with the other melee options for Pyro.