There's only 4 differences between MSI H270 Gaming M3 and MSI H270 Tomahawk Arctic:
1. MSI H270 Tomahawk Arctic is completely white in color with white LED over southbridge and it's great for white themed builds.
While MSI H270 Gaming M3 is black with red accents and LEDs that is great for black or black & red themed builds (like my Skylake build).
2. PCI-E x16 slots
MSI H270 Tomahawk Arctic: 3
MSI H270 Gaming M3: 2
3. PCI-E x1 slots
MSI H270 Tomahawk Arctic: 3
MSI H270 Gaming M3: 4
4. Audio codec
MSI H270 Tomahawk Arctic: Realtek ALC892 Codec
MSI H270 Gaming M3: Realtek ALC1220 Codec
As far as other features go, both MoBos are identical.
Specs,
MSI H270 Tomahawk Arctic...