What is a better motherboard Mini-ITX, micro ATX or Standard ATX?

Standard atx boards start at around $70, depending on the age of the chipset. Micro-atx start at around $50, so it's up to you as to how many slots you use and whether you want onboard video.

Standard ATX without contest. The extra pcie slot will become valuable over the year as you put more expansion card to the build.

it's a matter of preference my friend... micro-atx has become more popular, even with some enthusiasts... I see a lot of people with atx cases, but sometimes it's unnecessary... There are even people I've encountered that purchase the Maximus IV Extreme (1155) board for $350, and get a single card..supposedly to add another video card down the road, and it's foolish IMO..

Instead you could pickup a very nice matx case like the Silverstone TJ08-E and throw the matx Maximus IV Gene Z with similar features as it's bigger brother, but fewer fan headers, pci slots, etc... but, near identical overclocking potential for more than half the price
As I said..it just depends on yourself..I personally opted for a matx this time around and it's the best..saves space, looks great..and i dont need more than 2 pci slots if I have a 6990, gtx 590, or even a single gtx 580 with plans to add later..and even if I dont add another one down the road I saved hundreds by getting a matx setup...