Once you have made the choice to get started with ITX, there is still plenty to choose from. Just like any other system that can be built or put together, the purpose of the device is important. That determines to a large extent which processor is the right one, and that in turn leads to the choice of a motherboard.
First of all there is the processor, which determines the socket. If you already have chosen a processor, that is a foregone conclusion. Intel and AMD each have their so-called mainstream and high-end sockets. With Intel, these are socket LGA1151 and socket LGA2066 respectively, the former being confusing enough in two flavours. With AMD, the mainstreamsocket is called AM4 and socket TR4 is intended for high-end CPUs.
All these sockets are available on motherboards in the ITX format, except TR4, which is too large to fit other components. With a few exceptions, Intel's high-end socket is also unavailable, so most of the choice is in the mainstream segment. This is not a punishment, because with the processors available for this purpose from both Intel and AMD, you can handle the vast majority of workloads well. Gaming, office work, photoshopping, playing media and surfing the web are fine. For the heavier work, with video editing and video rendering as examples, the high-end platforms are more worth considering. On them you can use processors with many more cores - up to 18 pieces and accompanied by big TDPs. The question is if you still have to look at Mini-ITX. It ultimately depends on what your most common tasks are and how much money you can spend on the total system. You can keep it small and simple, or go loose with a small monster PC.
Once you have chosen a socket, the following is: which chipset? The chipset largely determines the functionality, such as how much storage you can connect and in what way, how many and how fast USB ports you have and with the latest boards even wireless network support.
On the Intel side there are the modern entry-level B360 and H370. These modern chipsets have support for USB 3.1 and wifi built in. H370 offers unlike B360 RAID functionality. Both lack the possibility of overclocking. This also applies to the older B250 and H270 chipsets - they still have to make do without built-in USB 3.1 and wifi, but sometimes and in this test field, respectively, separate chips are present.
If you do want to overclock, you will end up with the Z270 and Z370 chipsets. They also lack the built-in support for USB 3.1 and wifi, and in order to make a K-processor run faster you really need a Z chipset. However, we do need to make a comment on ITX. Because of the limited space generally a less extensive power supply is placed. Therefore, it is for the enthusiastic overclocker more interesting to consider a solid ATX board. If you simply want some extra performance without getting the most out of it, this is also possible on ITX - provided you take a Z-chipset. At Intel, B250, H270 and Z270 are limited to the Kaby Lake and Skylake generation processors, with up to 4 cores and 8 threads. If you want more, you can go for B360, H310, H370 or Z370: the eighth generation Core processors go up to 6 cores and 12 threads.
With AMD it's just a little bit different, there's the entry level chip set B350 and the more luxurious X370 and X470. The differences are less pronounced than with Intel; B350 has fewer built-in USB and SATA connections and PCI-e 2.0 lanes, and does not support a multi-gpu setup, but that doesn't matter on ITX. Overclocking is possible with both. ITX motherboards with the brand's A-series chipsets have not yet been tested. The AMD chipsets support processors with up to 8 cores and 16 threads.
Then there is the X299 chipset for high-end CPUs at Intel. On ITX it is a rarity, and some advantages of this chipset on a small size can not come into their own (like many PCI-e lanes). If you want more than 8 cores on ITX format, you can't avoid choosing X299.