Don't mind the "BRs suck cause they're amongst one of the few weapons in the game that requires any modicum of skill to use" crowd. Grab a Warden and be satisfied with every single kill you make.
Reaper is an Assault Rifle while the Warden is a Battle Rifle so you'll have two somewhat different results. The Reaper is great, it's essentially the Gauss SAW of assault rifles, but as an assault rifle its slightly more accurate. Thing works well at mid-long ranges and overall performs pretty well. However it doesn't really have any major advantage over the standard Gauss Rifle unless you really like the 200 damage per shot, 500 RPM fire rate. The Warden is very mediocre. It's a semi-auto and they've never really gotten around to fixing those so it's not terribly accurate at range and doesn't have the damage output to be good in close quarters. It's usable, but there are better options. If you're looking for something for ranged combat and aren't set on using a semi-auto, try the A-Tross or stick with the Gauss Rifle/Reaper.
The Reaper is a fantastic weapon, much more reliable and multi-use than the Warden. Both weapons require a great deal of skill however.
Well, I mean especially as NC, there is pretty much no range that battle rifles are better than your other options.
Well most of my experience is with the VS Eidolon with the added benefit of zero bullet drop but I swear by battle rifles in the field. They're not so good for storming bases but when out in the field or working with a group, battle rifles are incredible. I use high-velocity rounds and a 4x crosshair scope, lets me line up and drop targets peeking out from hidey holes all over the place. Another benefit, you can use it on Medic, Heavy, or Engineer while an assault rifle would be Medic only. This gives you a long range field combat option for any support work you might do. A sniper with the added benefit of being able to heal/revive, repair/resupply, or engage vehicles. The key is trigger discipline. Don't spam, your aim zeroes back to normal relatively quickly. A bit of patience and a little finesse will turn any battle rifle into a force to be reckoned with.
Weapons that cost more are NOT necessarily better, although it's a natural assumption. The developers' intention is that no weapon is straight up better than any other; they all have trade-offs which allow you to specialize in close-quarters vs. ranged combat, accuracy and mobility vs. raw dps, etc. As for why one weapon costs more than any other, who knows, but some very nice weapons are cheap (or free, as most of the default weapons are quite nice), and some pretty crappy weapons cost 1,000 certs.
Even the warden might be better on mid/far distance on the first look, the reaper is more versatile and you will fast recognize it also does well on far distance. Once you get used to it , the reaper is a beast! I promise If you are playing mainly medic, this weapon will pay out fast. Especially as medic you will find yourself often in battles where it comes to different situations when you try to support your squad (cqc, mid and far range fights). In my eyes the Reaper DMR is overall performing in all situations better. Maybe the 1st choice for a medic if you want to be ready for everything. Well, it depends alot on your playstyle what weapon you choose (like every other weapon). But i recommended it to alot outfit mates and they are all very happy that they got the reaper.
I'm not that unhappy with the warden, loved it, hated it. But it has it's surprise element on long to medium range. you can actually consistently headshot with it at range. Which AR just don't really offer the same way. This becomes more prominent when cover becomes a real factor. That said and done don't use the warden on a medic. use it on the engineer and the heavy. Up close it sucks. I think it needs buffed, but it has a purpose (Edit: medium long range battles with entrenched positions), it just adapts really poorly to a shifting battlefield.
Battle Rifles are excellent. All you need to do is turn a switch in your head that tells you to aim like you aim with LMG's and AR's, turn that to 0 and then turn that other switch that tells you how to aim with sniper rifles to 1. Then attach a 4x scope, compensator and grip and outcompete anything except sniper rifles after about 50 meters
If you can get headshots with a BR, you can also get headshots with ARs with the added bonus of headshot chaining that the accuracy-oriented ARs will grant you along with the inherent benefits of automatic fire. For the uncommon medium to long range engagements, I have found that ARs can still perform very well using a 2X scope without gimping your abilities when the fight gets closer.
I've only played w/ the Reaper in VR, but my god is that thing easy to use! With a comp/foregrip/4x/HVA the thing practically fires itself. Landing burst after burst into targets at 80-90mwas a breeze. It felt like it starts to choke after that though, I think due to its horizontal recoil. So I'm not sure if it's that viable past 125m or so. The only real issue I have with it is that it didn't seem to be much more accurate than the default Gauss, so why get it? But that's as much the Gauss's fault for its pure awesomeness...! The Warden may not be quite as effortless to use w/in 100m, but it keeps going and going well beyond that. Its effective range in skilled hands is about twice that of the Reaper (200-250m, depending). The Reaper may seem like a great weapon but I don't think it can compete w/ the Warden for long range work. For NC, the Warden is the true DMR.
You get it for the 167 minimum damage! That means 3 headshot kills out to render distance, and perfect ADS accuracy (unique among automatics) means it's easy to manage. It's my favorite gun in the game, it's the Baby SAW. The 200 maximum is nice but the 167 minimum is where the "holy hell this gun is an absolute destroyer of worlds" comes from. To be honest the Warden lacks a perfectly accurate first shot and requires the same number of headshots to kill at 100m+. I find that a gun that sacrifices potency at the 150m+ range to gain all the things a monster like the DMR does at close-mid is the preferred of the two. How often do 200m headshot duels really come up? If it's at anything like a decent sized fight you're going to be spending most of your time waiting for them to render The default Gauss Rifle is a great rifle, don't get me wrong, but it's a different beast entirely. It's a bit less accurate and a lot less damaging. It's high velocity and quick reload and good dps. It's an idiot-proof killing machine, perfect for new players.