Quino knows what he's talking about. I'll add my two cent's worth:
PCChips has actually been around since at least the era of the VLB (VESA Local Bus) motherboards for 486 processors. Anyone remember those? I actually still have some functional ones, hehe. Well, PCChips was REALLY notorious at one point for putting FAKE CACHE CHIPS on their motherboards. Remember that this was back when L2 cache was on the motherboard and 486 motherboards would have banks of DRAM cache chips.
Amptron has been around since the 486 CPUs also. I don't know how far back the two companies go. Amptron had some decent 486 motherboards. Starting with their Pentium motherboards, the quality went downhill. Now, this was before I got into "performance" so all I cared about was that it worked. Amptron Pentium boards died, and died often. I remember once scoring a great deal (this was also before I realized that "you get what you pay for") on some Amptron Pentium boards using the OPTi Viper chipset. 4 out of 7 died within months. Now, since some of their boards are really rebranded (some even use same model numbers, haha) ECS-et-al boards, I may try them out again. I do recall, even way back when the 486 was king and Pentiums were just a wet dream to be had for thousands$$$, at that time Amptron already had a website going with support documents, the works. Unfortunately at the time their site was extremely slow. But, few other motherboard manufacturers probably had web presence at the time, including full documentation. Amptron is also good about accepting RMA's (but probably due to their boards needing it so much at the time, haha).
Alton - this name is associated with the whole conglomerate somehow. They have a P4 board that is bright-red, while the ECS version is purple.
ECS - their boards seem overall to be decent. No "enthusiast" boards, just inexpensive ones that worked. Maybe the exception is the K7S5A which had a lot of teething problems. They may soon be getting into the "enthusiast" market, with the announcement of upcoming boards with Vcore adjustments. Also, they have started to use "cool" colors for their boards, such as black and purple.
If you compare products from these companies, you'll find identical boards with sometimes different part numbers and PCB colors. Packaging is different and sometimes the Alton/PCChips versions will include the impossible-to-find AMR/CNR cards.