I will upgrade my RAM and I will go for 16GB. I would like to ask if its better to go for 2x8GB (dual channel) or 4x4GB (quad channel)?
Depends on your mobo. If you have quad channel confg. you surely get an advantage over the quad channel.Honestly speaking, There is a small (very small) performance gain but you will only really notice it in benchmarks and programs that can actually take advantage of it, which aren't many...
But again , if your board supports quad channel (which obviously it does otherwise you hadn't asked the question , i guess ) go for it.
Motherboards offer dual channel, triple channel or quad channel depending on the chipset used..... what you buy depends on what board you have. If you put 4 x 4GB in a dual channel board (i.e. 1155) it does not make it quad channel.