These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The CAWS will ruin anyone's shit in vanilla JA2. In 1.13... it just got deadlier.
Not always, as 1.13 introduced "readying" costs, so heavy weapons often subtract AP while aiming, often only allowing one or two not-very-well-aimed shots. Combine that with the not so great range, it can quickly become Awesome, but Impractical.
Sniper rifles and rifles. For the latter, anyone within your range is going to die, even with a Winchester '92 (which has a pitifully short range, comparable to that of pistols). In the case of the former... the Erma. Just... the Erma. It's so accurate, even a non-sniper with average marksmanship can out-snipe Scope with it, and it's only a touch below the Barret (the strongest sniper rifle) in damage, with a much better range and weight.
The ACR, G11, or FN-SCAR-H Sniper variant. Both are accurate, versatile, and damaging; the only downside being finding G11 and ACR ammunition.
AET, "cold-loaded" (subsonic), or match ammo. The only downside for AET rounds is that the weapons they're used from degrade faster, while cold-loaded rounds have less penetration against body armor. Match ammo performs against body armor about as well as regular ammunition, but is more accurate, letting you get headshots more easily.
Mortars, mortars, mortars, oh, and mortars. Bad thing is, it'll go both ways - you can easily decimate a 50+ invasion force with only Barry, Red, and Fidel casually lobbing shells at the bunched-up goons, or your EOD armor-wearing strike force can be literally reduced to ashes.
Among the v1.13 weapons, the MP7 = best sidearm in the game, period.
So do the FN P90 if you prefer More Dakka instead of Guns Akimbo (and if you like either of these, then I'd assume you always fight at night). Some mooks do have them now, so you can easily get a reload.
Same with Metal Storm's Surf Zone, the best thing to hit CQC weapons. Fire and the person in range is DEAD. DEAD. DEAAAAAD!!
One key change in v1.13 is that by default, income will not decrease when you stall your overall operations against the Queen's army. Enrico will still get fed up if you hole up (i.e. in Drassen) and send you angry e-mails, but your account is credited the same amount of dollars, based on your holdings and local support. This allows you to hunker down, i.e. to stockpile weapons and supplies from Bobby Ray's online shop or to train your members... some of whom will need it.
And of course you can edit your starting funds. Say, start with 10 mil in day 1.
Not just the guns, but some attachments do count. To start with, the Aimpoint Projector gives quite a ridiculous aiming bonus. And later, the Rifle LAM Flashlight combo which have less aiming bonus, but compatible with more weapons and have a slight vision bonus at night.
The Insight-2000 will fit any gun, and is a choice for rifles that can't accept LA Ms. Couple it with a ACOG-Reddot combo. You're guaranteed to hit a lot of things.
The Old Aimpoint Projector is balanced out in 1.13 by the fact that it fits a grand total of three rifles: the G3, G3KA4, and the G41; and all three rifles are only decent at best. In particular, the old 7.62mm rifles—particularly the FN FAL variants—have lost their gamebreaker status in the latest 1.13 builds, which incorporate aimed autofire (a feature not present in the original game) and heavy recoil. For ranged automatic weapons, there is suddenly a reason to go back to the 5.56mm rifles: the recoil of the 7.62 NATO weapons is too heavy to be of practical use in automatic fire. (Unless you get a grippod/foregrip.)
The OICW - while, in statistics, appears to offer the same range/accuracy bonuses as an ACOG-Reflex-Insight LAM combo, is far more accurate than it lets on.
The XM 8 marksman variant is the only assault rifle that allows a sniper scope - less readying costs than most sniper rifles, for obvious reasons. Mercs with a decent accuracy score can regularly score headshots.
In Unfinished Business, Charlene "Raven" Higgins. You only need to pay mercs once when you hire them in this game, and Raven offers a ridiculous bang for the buck. She is among the best snipers in the game, and much, much cheaper than the only two better than her (Lynx and Scope). Outfit her with a powerful sniper rifle and she will one-shot almost everything from ridiculous distance. She is, in fact, so powerful that a lot of players at the time considered it almost cheating to bring her along.
A surprisingly subtle one: Leadership plus wisdom. High leadership helps boost morale. Deputy/Squadleader (in 1.13) further boosts it. But high wisdom lets your poor-leadership mercs develop that particular skill very quickly, and once you've got several regular mercs with good leadership alongside Deputies and Squadleaders, the morale across your personal army will be sky-high, which in turn greatly boosts everyone's performance in combat. Even the piss-poor MERC mercs and the weaker RPCs will be regularly hitting targets with deadly accuracy.
Germans Love David Hasselhoff - The series is highly popular among Finnish PC gamers with Jagged Alliance 2 getting voted Game of the Year by both the readers and the editors in the largest gaming magazine in Finland. It also was among the best-selling PC games in Finland for months. In fact, in Finland Sir-Tech is mostly known for Jagged Alliance series rather than Wizardry.
Ho Yay: If MD and Danny work together for a while, MD has some...complimentary things to say about Danny that can readily be interpreted this way.
The Cambria hospital, especially in 1.12. The game isn't built for in building combat, causing mercs who open doors to put their entire body in front of the door and eat lead from an interrupt given to the enemy on the other side. A lot better in 1.13, as the new AI will cause most of the enemies to investigate the lobby (which is where you've most likely shot someone), but chances are, there's one or two enemies that hole up in the cafeteria or the room in front of it. Fortunately, you do have one big advantage: Bobby Rays' entire explosives catalogue, which can open up all kinds of doors.
Tixa Prison's basement is a tight mess of corridors with enemies firing from behind slitted or barred windows. Bring a few LAWs; you'll need them to root the buggers out.
Orta's labs render some of your most common tactics to deal with tight corridors impossible with all those indestructable walls and that one chokepoint at the end of a long hallway, through a single narrow doorframe. The enemy elites love pouring automatic fire and grenades into that tiny room before running in with knives that go right through your Spectra/EOD armor.
The Scrappy: Some of the mercs added by the Wildfire expansion, mostly because of a combination of sub-par voice-acting, bland characterization, and Character Shilling. Plus some of them replace better characters in the regular game's roster.
The Woobie: Elliot, as the result of being the frequent victim of Shoot the Messenger, literally in the end. Though seeing as that doesn't do squat to hinder him in his diligent if unappreciated service to his beloved queen, he's also a Determinator.