Think of any seat in the 400s as a continuation to the seats in the 300s. So the 300s are much better seats to have for a Hawks game. The 400s would have been fine for a Thrashers game back in the day when hockey was still in Atlanta.
Our seats for the particular game we went to (Hawks/Heat) were near the top of the arena in row K. Row C was the very first row but in those seats, your view may be slightly obstructed due to the railing.

In 408, you will even be looking down at the scoreboard at center court. Section 408 is a great way to go to see a basketball game for cheap but don't expect an intimate experience with the game if you sit here.

The food prices were outrageously priced as I had anticipated but the food selection was definitely above par.
Just so you know, all of the entrances are called "Portals". Not sure why they chose that name but it works.
There is a Marta Stop just outside of the arena site so it's easily accessible from the central business district in downtown Atlanta.
Tons to do in the surrounding area too from the Olpympic Park, CNN Center to the Luckie Marietta District. You can go to a Hawks game and keep having fun afterwards if you so choose.