Interesting topic here.
The question being: which brand is the best.
Basically there are two types of memory modules: original and non-original brand. Original modules are modules manufactured by the original chip makers. For example, Micron builds an IC chip, and then manufactures the module. The module becomes Micron on Micron, or Micron original. For other third parties, other than Micron, that build "major-brand" modules, the modules they build are considerd 'on third'; Micron on third, for example. Manufacturers who label their own chips and build modules are considered as OEM (original Equipment Manufacturers) manufacturers. Typically OEM manufacturers will use "non-major-brand" chips to build thier modules, often refered to as UTT (UnTesTed chips). UTT chips cost less than major chips, but the quality is not as good, because major-brand chips are more thoroughly tested.
Original modules typically always have better quality and performance at standard latency.
Also one more factor to consider: Latency. Original modules follow standard latency. For DDR400 the standard latency is CL3 (3-4-4 or 3-3-3), for DDR333 CL2.5, for DDR266 CL2.5 or CL2.0. Typically retailers will buy original chips and manufacture the modules themselves. To market the modules, the retailers will lower the latency, and this is ultimately what the consumer pays for. Not such an easy task to do. Many retails perfrom extensive testing finding the right chips, PCB board, & best safe operating latency. The testing will be done on specific systems and they will guarantee safe operating latency for certain motherboards. Thus, you could run into issues using mothrboards that are not recomended.
The largest Memory manufacturer is Kingston. Kingston, Crucial, Mushkin, OCZ, Corsair and Geil for example, are all memory module manufacterers, and do not typically sell original modules to the retail market. In addition, they do not manufacture memory chips. Only a handful do: Samsung, Micron (Crucial), Infineon, Hynix, Mosel, Elpida, and Nanya are the largest chip manufacterers; there arent many others.
If we are talking about original modules, Samsung original is the most sought after modules. The returns on Samsung modules is much lower than most other brands. If we are talking about market share, Samsung owns close to 30% making them #1, so it makes sense that Samsung can maintain such a facility that offers high quality memory. Micron and Infineon owns about 20%. Right now Sansung is #1, Hynix #2, and Micron Infineon both competing closely for #3 spot in the DRAM market.