Actualy alexoiu is incorrect better 4x4 why?Thats becouse more speed i mean if you choose 2x8gb for example if one stick speed is 1333mhz total for these sticks you get 2666mhz but if you go with 4x4gb 1333mhz each it means its gona be total of 5332 mhz which means its gona be faster there is no differece betwen memory 4x4gb gona be faster than 2x8gb
Hmm...it depends entirely on the kits you're comparing. 8GB/stick non-ECC produces more errors than 4G/stick RAM. 'IF' you'll need 32GB then 8GB/stick is obvious. Next, RAM's 'performance' is determined by the IC's used (Rated frequency, CAS Timings, voltages, etc).
Also, if 'later' then I'd probably look for a very popular kit that's going to have a long shelf-life.
Example of a good 2x4GB that 'should' be around for a while -> Corsair CMZ8GX3M2A1600C9 - http://www.newegg.com/Product/Product.aspx?Item=N82E168... ; note there are several color versions which all have the same IC's. The CMZ8GX3M2A1600C9 kit has proven itself to be stable and have a low error rate.
Keep in mind all RAM throws errors (1-2 errors per month) and 8GB is higher. While 'ECC' RAM can correct these errors non-ECC cannot. This brings me to the next topic of 'use,' if you're a professional then I'd consider a Xeon and ECC RAM the cost isn't too much more but the end 'product' will be error free.