1) 99% personal preference. I believe magnets offer slightly better conductivity, but if you're building 1.0-1.4Ω you're not going to notice much of a difference. Some feel crunchy with magnets, others feel crunchy with springs... It all boils down to the clone you get.
2) Silver > Copper > Gold > Stainless steel. Silver and copper will tarnish over time and require cleaning to maintain conductivity, where as gold and stainless steel do not (though cleaning never hurts, since tarnish isn't the only thing that causes voltage drop).
3) Everywhere... 88evapes is good if you want cheap, but the clone I got from them is fairly low quality. I've heard good things about 101vapes and fluidvapes, but can't speak from personal experience. Fasttech is regarded by a lot as a good place to go... Only ordered from them once over a month and a half ago, I'm still waiting on my stuff.
As for the company... A lot of this will vary on a clone-by-clone basis. For example, let's look at the Black Stingray mod. From what I've heard, Infinite has the best version (aesthetics wise, engravings are done very nicely... Magnetic firing pin, floating 510 connection). hCigar's clone has the same features, but the engravings aren't done as well. Other clones out there either don't have the magnetic firing pin, and/or don't have a floating 510. Unfortunately, there's no real set hierarchy in terms of companies and their clone qualities... It's all going to boil down to the specific clone you're talking about.
Also, I'm kinda curious... Since you're building at 1-1.4Ω, maybe you should just get a nice regulated mod? It'll be a lot safer and provide you with a more consistent vape... No worrying about over discharging batteries, your atty developing a short from being bumped the wrong way, etc. and you'd get just as much if not more power from it.