Comment by somat

Samsung, SK Hynix, and Micron are the only three manufacturers doing leading-edge DRAM manufacturing, but there are other companies like Nanya that do older DRAM types and specialized DRAM parts for eg. embedded and industrial applications rather than PC, servers, and phones.

As for who makes the best RAM, it changes from one generation to the next, and also depends on what you consider "best": you might be looking for chips that overclock well in a desktop, or that are least likely to suffer compatibility issues and performance loss when maxing out the capacity in a desktop, or maybe "best" might mean who has the lowest-power LPDDR for your phone.

The DRAM parts made by the big three largely all adhere to the same standards (thought not necessarily all supporting the same frequencies), with the most significant recent example being GDDR6X that was essentially a NVIDIA-Micron exclusive partnership. For the most part, it's the latest iteration of DDR (desktops and servers), LPDDR (handhelds and low-power laptops), GDDR (GPUs), and HBM (more expensive GPUs).

SK Hynix is winning in DDR5 land - their memory performs significantly better in all respects compared to Micron and Samsung.

Whether that matters much is debateable - maybe they get higher yields as a result (since more chips are sufficiently performant to be useful) but JEDEC specs seem pretty generous relative to what you can achieve on consumer platforms, so I somewhat doubt much RAM is thrown out because it's too slow to meet spec.

It's pretty random, though. Back in DDR4 days Samsung produced the best memory (B-die) and it wasn't particularly close - near-DDR5 speeds with lower latencies. At the same time, some of their other dies (I guess from other fabs?) was absolutely awful.

Again, I don't know how much that translates into profit though, since the performance user market for RAM is probably a fraction of a fraction of the overall memory market.

My sibling comment has a lot of good info, but to answer your question for ddr5, SK Hynix makes the ram capable of the highest frequencies/best timings, Samsung is second and micron is third. At least this was true when ddr5 initially came out, these things could change. Its also worth mentioning that manufactures can have different grades/product lines so there is variation within a manufacturer to. My perception is that Micron and Samsung are cheaper than SK Hynix, though idk what wholesale prices actually look like.

The "best" depends on what you want. For example, with desktop memory the previous DDR4 gen Samsung's B-die was considered the top choice if you wanted the fastest speeds and highest overclocking potential. Micron's rev-e die was also desirable as it was usually dual rank (technically slower, but for certain real world applications you will get better performance) and also overclocked quite well.

Now with DDR5, Hynix's A-die is considered the best option.