Hmm...I just did some more research and found the mATX is basically the same thing as an ATX setup, but with lesser things, but I might actually be consider the SFF approach.
According to my research (through Wikipedia) I have found the mATX is basically in between SFF and ATX. SFF is more like a shoebox design, but a bit more height.
What architectures allow gaming? That is the more important question for me. I do realise that if I will be gaming on SFF then it will be more noisier.
Also, where do I find parts for both configurations (mATX and SFF) (I maybe be building more than one computer for the future: mine is definitely going to be gaming oriented, but there are going to be at least another two (for sister, and the other for my parents) that will not need any gaming parts whatsoever).