To address the OP's original question: number 1. Much less likely to have problems, just buy from a quality manufacturer.
Now for a bunch of stuff you didn't directly ask about, but has been discussed.
If you're running a dissipater you gain one for sure advantage, a longer sight radius. Arguably you gain better reliability with a rifle length gas system, but this is debatable, and is also based on how well the rifle is put together.
The improved accuracy is a moot point if you're talking HD ranges. You can just as easily put an entire magazine into a 1" square at 15 yds with a carbine length sight system as you can with a rifle length system. I doubt many of us have homes where an interior shot will be longer then 15 yds. Now if you're planning on doing some distance shooting, then the longer sight radius can become useful.
The reliability of your rifle is largely a function of build quality. You can have an A2 spec 20" upper that barely runs or a 7.5" NFA that never hiccups. Buy or build quality and it'll run. In any of the standard barrel lengths (14.5, 16, 18, 20) you can run any of the other gas systems reliably. You might be cleaning/lubing more or less for your personal rifle, and you may wear springs out faster but it should run. If it doesn't send it back. There is no excuse these days for rifles that are unreliable.
I personally HIGHLY recommend putting an optic on your rifle. If you want something that is rugged and you can forget about, put an aimpoint Comp M4 on it and change the batteries once a year when you do your smoke detectors. Leave it on the rest of the time. You'll have an extra year or two of battery life in case you forget. You can become very fast and proficient with irons, I'm certainly not arguing that. However compared to a good optic, they are slow and hard to use. They do not tolerate shooting out of position well, and they require contrast to use. All black sights on a black target are hard to make out, even in daylight (hence why the 6 o'clock hold is popular in High Power shooting). An intruder wearing all black will present the same problem even if illuminated. Night sights help with this, but still require a lot of practice to use in unconventional positions. I personally like the EOTech, but you can't go wrong with Aimpoint, EOTech, Trijicon, Meprolights, or Insight Technologies. Along with this, if you go with a rifle with a fixed carrying handle since you only want irons, you'll be screwed if you want to add an optic later. If you must have a carrying hand, get a removable one. I recommend getting a standalone A1 style rear sight if possible. Daniel defense makes a good one. You're not going to be dialing in elevation as you shoot a know distance target table. The elevation knob is just one more thing to get bumped or turned that can affect your accuracy. Set it once and forget about it unless you change ammo types, or really bang up your rifle. Even then it'll probably still be pretty close.
If your putting a light on your rifle you're going to need either one that rail mounts, replaces your hand guards, or is attached to a VFG. Trying to hold your rifle and manipulate a light is a no go. Can it be done in an absolute emergency, yes but it sucks. Don't do it. The Surefire M500 is the top of the line option if you choose to replace the hand guards, it is expensive, heavy, but very reliable. The Surefire M900 is the top of the line option for a VFG/light integration. It is expensive, heavy, reliable, and puts your hand to low from the bore to be very stable (personal opinion). For rail mounted there are of course a ton of options. You can get little add on pieces of rail if you want to run standard hand guards, or you can go to a full rail system. It sounds like you're looking for something along the lines of the add on pieces. You might try a rail section that mount to the front sight base sight tower. This leaves the hand guards smooth and gets the light out towards the muzzle were you need it.
I'd say based on your original description get a M16A1 style rifle (20" light weight barrel with a fixed carrying handle and A1 sights) w/ titrium night sight inserts, use a front sight block rail insert and mount a good light. I personally would recommend going with a 16" flat top upper, with a light weight barrel, A1 style rear sight, titrium night sight inserts, non magnified optic of some sort, and a front sight block rail insert and a good light.
-Jenrick
As an aside on suppressor (please note this is all based on Texas law). There are multiple culpable mental states that are used in the penal code to describe the required mental state of the actor. Intentionally is the highest of these, meaning the actor acted with full knowledge of the consequences of his act and intended these consequences. Deadly force is normally defined as "capable of causing serious bodily injury or death." You can not shoot someone in the foot and say it was less then deadly force. If you intend to shoot someone and do so, you are intentionally using deadly force, period. A firearm is deadly force (by definition), the shooters choice of targets is immaterial under the penal code.
Intentionally using deadly force, intentionally pulling the trigger, means that you have to be able to justify the intent. Using a suppressor, hollow points, match trigger, etc. are meaningless. If you accidentally shot someone they might matter, but you've already said you intended to use deadly force, and did so. You go to court to articulate the intent of the shooting, "to stop a threat of serious bodily injury or death to myself or a third party". Note that this allowed usage of deadly force (chapter 9 of the penal code) matches up with the definition of deadly force. Basically if you feel, you or another, are about to be subjected to deadly force, you can respond in kind (there are other allowed usages, but they aren't relevant here). What gear you had on your weapon, what ammo you used, etc. is not relevant. In short putting a suppressor on your rifle isn't a big deal. Again note all of this is based on Texas law.
