I have used both an adjustable gas block (agb) and a configurable buffer kit to tune an AR-15. The problem with threads like this is that they are absolutely confusing for people who haven't dealt with this before and are trying to figure out what to do or what is involved. If it was as easy as, "H2 worked for me!" - then that is all that would need to be sold. Unfortunately, it is not always that simple. There are so many AR gas system configurations and barrel lengths. A person is tuning their AR either by reducing the gas flow via an agb or increasing the buffer weight.
I like the adjustable gas block. It goes to the source and reduces the volume of gas used to cycle the rifle. It can adjust from no gas to full gas. There are drawbacks too. First, is cost. By the time you buy the agb, gas tube, roll pin (if needed), you have typically spent over $100. That is without eventual rebuild kits (depending on what kind you get.) Remember that the burnt powder carbon rich gas has to go somewhere, which is typically through the threads of your agb adjustment screw. Secondly, you have to put everything together and tune it. Remove muzzle device, probably the handguard, pull of the current gas block and gas tube, assemble the gas tube on the agb, place the assembly on the barrel, and make sure the new block is aligned with the gas port.
You're done, right? Not yet, because now you have to adjust it and tune it at the range for the ammo you want to use. Most of the time a person sets it with a little slop for colder weather or some margin with lower powered ammo. However, if you have it set for a certain ammo and decide to try something a lot lower or higher powered, now you are back to adjusting it again. Hopefully, you will remember which way to adjust for more gas or less. If not, you may end up practicing your pogo-ing skills - haha.
The buffer weight solution is simpler in some ways. If you guess right at what you need and buy a H1/H2/H3 buffer, it is as simple as pulling the takedown pin, depressing the buffer retaining pin, and replacing the buffer. Of course it does not affect the excess gas going through the port, but it is a quick solution for usually $50 or less and you didn't have to take the upper apart.
Maybe in today's day and age there is some sort of calculator that takes variables such as: ammo, port size, gas system, bcg weight, and buffer weight into consideration so that you can be right the first time. (Remember that the military chooses their buffer requirements based on knowns - their specifications for ammo, gas system, barrel length, gas port size, etc.)
If you guess wrong, and only have the one buffer with you (ie - the one in the gun), you will not have a fun range day. With this method, it is better (IMHO) to buy the kit and have at least two buffer weights made up already. Changing weights in a buffer is driving out one pin, using a padded clamp or vice to pry off the buffer bumper, and replacing between 1 and 3 of the steel weights with tungsten weights. Push the bumper back on, drive the pin back in, and you are ready to put it back in the gun. If you have a few guns that need tuning, just buy the tungsten weights and the solution could be as low as $30 per gun.
I won't go too far into this, but if you are the guy with one lower and several uppers of various calibers, then it's about how much money you want to spend. AGB's for "all your uppers" will cost a lot, but will be very simple, since the gas setting is set per the upper. OTOH, with no agb's and adjusting via the buffer weight, you are always having to remember which buffer you need for which upper (or just bringing them all, JIC).
Short story is that I have used both and both ways work to tune an AR.