The Taichi is a better board in terms of features imo, I'd rather have dual M.2 slots personally.
I presume you're talking about the X370 Gaming 5?
Both have the same sound chip; the Realtek ALC 1220, although the Gigabyte mentions in specs it has TWO of them, which is a little baffling tbh, i'm not sure if that would offer much improvement if any, never seen it before on a board.
The Gaming 5 has a 10 phase power design while the Taichi has 16, and both support up to 3200MHz RAM.
The Taichi also has .ac wifi on board as well as BT 4.2 which is a bonus, and makes use of Nichicon caps which is a tick in my book. If you have an S8 I believe this allows for bluetooth connectivity to your system, allowing you to get texts, updates and notifications in Windows which is pretty cool.
The Asrock has 1x Type A 1x Type C USB ports while the Gaming 5 has the same.
The Gigabyte's other rear USB ports are a total of eight other 3.0 USB connectors, two of which are 2.0, four of which are 3.0, and another two of which are 3.1, while the AsRock holds 6 rear USB 3.0 ports in addition to the type C and 3.1 Type A connection.
Both are equally fantastic, if you feel you'd use all of the rear I/O effectively, i'd get the Gigabyte, otherwise the AsRock seems like a better choice to me due to that M.2 storage.
Both boards then have 2x 3.0 and 2x 2.0 internal headers, so no diff there.