taliv gives good advise. Don't go swapping things around just because you're looking for something to buy that will supposedly make things better.
Yes, you can change the weight of the buffer that you are using to tailor the way the rifle shoots and to alleviate small problems. In a lot of cases, these problems are either due to weak ammo that will cause the rifle to short stroke, so you can go to a lighter buffer; or in the other extreme you may have a rifle that is overgassed, which could cause extraction issues (like with steel cased ammo). In this latter case, you'd go with a heavier buffer.
Generally speaking (assuming that everything is in spec), the higher the gas pressure the heavier the buffer for smoother performance. So...for a 16" barrel with a carbine length gas system, an H buffer wouldn't be out of the ordinary or even heavier. The same barrel with a mid length gas system will operate at a lower pressure so you might be able to get away with a lighter buffer. A 20" barrel with a rifle length gas system is going to have even lower pressure, so a standard buffer is likely all you'll need.
Just as an example, my last build was an 18" barrel with a rifle length gas system. This system operates at low pressure and has a pretty short dwell time (determined by the length of the barrel between the gas port and the muzzle) so it shot mild with just a standard buffer. It also did well with an H buffer, but wouldn't cycle cheap ammo at all with a H2 buffer.
Personally, I've settled on the Spike's ST-T2 buffer for all of my rifles. It seems to be just the right weight. I don't know how much they weigh or why they work in all of my rifles. They just do.
A pretty good indicator of whether you are using the right buffer for you is to watch your ejection pattern. If you're brass is ejecting forward at the 1:00 to 2:00 position, you have a lot of gas pressure and a pretty high bolt velocity going on. Try going up on your buffer weight. If your brass is ejecting at the 4:00 position or further behind you, you have too little bolt velocity, try going to a lighter buffer. If your ejection pattern is something around 3:00, you're just right. Don't mess with it. All of this assumes that all else is well with the rifle.
Changing a buffer will likely not cure problems like a way over sized gas port, a bad gas leak or rings on their way out.