There's much that can be said about how to build your Ranger team in Wasteland 3, but as we all know, character builds are just half the story. The other half of the story is the gear that you bring into battle. After all, having a highly optimized character build does nothing if the weapon that you're using is hitting for 10 damage per hit at the end of the game, and having a gun that outputs hundreds of points of damage per shot doesn't particularly help if it takes an entire turn to shoot. Things get slightly more complicated when you factor in weapon attachments, which can often drastically affect how a weapon performs. There's also certain unique weapons that, while good on their own, belong in their own ranking tier when a character is built around the weapon's unique properties.
Naturally, all of the good weapons in Wasteland 3 are progress locked. You generally need to meet Angela Deth in person for the first time to unlock these weapons at Ranger HQ's armory, or a vehicle chassis capable of withstanding level 3 radiation. Thus there is some merit to just rushing through the quests involving the Patriarch's sons and then mopping up the side quests. Fortunately, this means that acquiring many of the best endgame viable weapons is a rather straightforward matter. Unfortunately, you can't reliably get more than one copy of each endgame weapon, and weapon attachments can't be removed, so it's rather important to have an idea of what you want to do with said weapons. This is where reference guides (such as this one) can come in handy.
Note that for the below weapons to reach their full potential, it is assumed that you have maxed out Coordination and Awareness. Unique weapons that are only found in Yuma County are not mentioned because if you can clear Yuma County to begin with, you've basically already beaten Wasteland 3. Melee weapons are also not mentioned because they're fairly straightforward to build around.
Background: Disciple of the Metal
Skills: Big Guns, Toaster Repair, Weird Science
Required Weapon Mods: Incendiary Linkage, Shortened Barrel, Quickfire Mag
The Minigun is a fairly good weapon on its own, capable of throwing out bullets like it's going out of style, but it gets even better when it's modified specifically for a Ranger who specializes in incendiary damage. The idea behind this weapon configuration is to use the Shortened Barrel mod (+20 damage per shot) to get an extra 360 damage per attack. Converting the Minigun to do incendiary damage then applies a 10% loss of damage per shot. However, this is more than compensated for by the 70% damage buff from the aforementioned character build. This leads to approximately 1400 base damage per attack, which is more than enough to tear through anything, regardless of if it's machine, man, or monster. Throw in the Quickfire Mag and you can squeeze off at least two attacks per turn, assuming that you don't move and have at least 12 AP.
You can also create versions and builds that revolve around explosive damage, but then you lose the synergy with flamethrowers. Other potential substitutes include using the Titanium-Cobalt Barrel (+8 damage per shot) if you can't purchase the Shortened Barrel from HOGS at the Denver Ruins. If you're really worried about how robots resist incendiary damage, you can also throw in the Mechanics Skill, but you generally don't need it.
Required Small Arms Perks: Clear Cover, Devastation
Optional Skills: Explosives
Optional Background: Explodomaniac
Optional Quirks: Sadomasochist or Pyromaniac
Ideal Weapon Mods: 38MM Magnifying Scope or Farsight Computer Assisted Scope, Open Cylinder Choke, HE Fuse Linkage
Wasteland 3's Small Arms weapon upgrade path for shotguns is fairly logical for the most part. By the time that you reach Aspen, your best options are going to be either the Tactical Shotgun or the Assault Shotgun. The former does more damage per shot, but the latter fires three times per attack at the cost of two more AP. Thus you must choose between AP efficiency and raw burst damage.
Then comes the Jackhammer, arguably Wasteland 3's most "overpowered" weapon. It does more damage per shot than the Tactical or Assault Shotgun, but it only requires three AP to fire a burst of three shots. This means that each shot basically only costs one AP. If that's not enough, the base overall damage profile is roughly comparable to the top-tier Sniper Rifle, the Eliminator, which costs six AP to shoot. Combined with the Devastation Perk from the Small Arms tree, which buffs shotgun damage by 25% for each target hit per shot, the Jackhammer turns the Ranger who's wielding it into the ultimate crowd-control weapon. It's so good that one would suspect that the wrong AP cost was entered by the developers because there's no way that such a weapon requires so little investment to do so much damage.
If you really want to push the Jackhammer's damage, convert it to an explosive weapon and invest in the appropriate character build. This has the side effect of helping with armor penetration, making an already powerful weapon near unstoppable.
Skills: Automatic Weapons, Explosives
Quirk: Serial Killer
Where to Find the PDW-01: Hidden cache in Massacre Site, northwest of Yuma County on the world map
SMGs in Wasteland 3 suffer from low penetration and somewhat poor ammo efficiency, but the PDW-01 completely turns that around by having built-in explosive damage. It also has relatively hard-hitting bullets and a decent magazine size, making for a very versatile weapon that can be modded into quite a few configurations.
Now you may be wondering why would you use the PDW-01 when the Ripper exists. The Ripper fires four more bullets per attack, meaning that it has great synergy with weapon barrels that provide a flat damage buff, and a better crit multiplier. You can even convert the Ripper to an explosive weapon for roughly the same overall damage. The main thing that sets the PDW-01 apart is the fact that you almost never have to reload, whereas the Ripper must reload after three to four attacks at most. This absolutely clashes with the AP manipulation offered by the Automatic Weapons Perks and Serial Killer, which is designed to enable kill chains, not reloads.
Background: Goat Killer
Skills: Sneaky Shit, Sniper Rifles, Mechanics or Explosives
Unlike all the other weapon classes in Wasteland 3, sniper rifles are so straightforward that it's barely worth mentioning. This is doubly true at the endgame, where there's really only one sniper rifle that's viable: the Eliminator. That being said, having a straightforward upgrade path isn't necessarily a bad thing as it simplifies logistics and it lets you get creative with weapon mods and builds. For example, the most popular way to set up a dedicated sniper is to have them max out on crit chance and crit damage multipliers. Combined with Sneaky Shit and a Phase Silencer attachment, you can easily hit for thousands of points of damage on an opening attack.
In addition, there is some synergy between the average crit sniper build and Explosive weapons as they both benefit greatly from crit damage modifiers and they're both excellent choices to initiate combat. Needless to say, an explosive Eliminator with the Explodomaniac Background is quite viable too. The cherry on top of it all is the fact that it's a trivial matter to fire twice in one turn once you max out your Coordination. On the other hand, Explosive weapons themselves have slightly better AP synergies with other weapon classes, so it's really a question of whether or not you want to max out one Ranger's damage or the whole team's damage.
Skills: Weird Science, Automatic Weapons
By now, it's no secret that Wasteland 3's assault rifles are essentially trash tier. They do almost the same damage per shot as SMGs, but fire only half as many bullets per attack at best, and they have no particularly noteworthy Perks. The sole exception is the Atom Smasher, which fires five times per attack and offers a decent amount of damage per shot. You're still not getting as much damage as SMGs, especially since you can't manipulate your AP costs, but it is a reasonable choice for fighting robots and other mechanical enemies. Pair it up with the Polar Vortex and you've got as reasonable an assault rifle build as you can get.