I think this is the most important order for me. 1, Brand / Quality 2, compatibility 3, Performance 4, Price 5,Esthetics last
1. Price. 2. Heatsink Design (I will never buy RAM with tall heatsinks again, it's not worth the hassle with a cooler). 3. Voltage. Price because I'm tight, performance and brand isn't too big a deal since latency doesn't have much effect in real life with fast DDR3 also most RAM brands are good anyway so I don't stick to a certain brand. And I'd prefer to get as low voltage ram as possible since running into a problem with overheating memory controller.
For me it's probably, Frequency, Brand, Price, anything else is just something i decide when i buy it. Not to say that the frequency has to be the highest that can be bought, just the one i want e.g. 1600mhz. I've bought corsair for ages and never gone wrong so I like to stick with it. Price, the cheaper the better.
For me its the following, 1 being the most important: 1. Brand- I only buy corsair's RAM as I've always used them without any problems, there support and products are top. 2. Frequency/Lantency- this also matters, i tend to pay more for lower lantency and high frequency, but this depends on the price difference. 3. Warranty- The other reason for me sticking with Corsair is their lifetime warranty.
I think we've been around this "lifetime warranty" issue before: "We guarantee this product to work until it doesn't".
@Bindi - If you would be doing a review of memory modules, could you please include this kit (http://www.yoyotech.co.uk/item-detail.php?products_id=3301100)?
When ever I buy hardware the main things from 1 through 5 are the price/value. In memory especially I just tend not to care about much else. Just pick the cheapest kit with any reasonable clock speed/timings.