3rd Floor of the Tower.
Contrary to the 1st and 2nd Floors, the 3rd one was vastly different. For the first, unlike the first two floors, people with higher strength than Bronze-Tier were rare here. One could say that the 3rd Floor was calm one, without any "problems" like the 1st Floor or 2nd Floor, even though it was certainly unique in its own way.
Basically, only the 1st and 2nd Floors had people from all Tiers in them, while the rest of the Floors didn't. Even among the whole Tower, one could say these two were unique in their nature.
The previous ones were special due to their nature, especially the 2nd Floor. Usually, the higher the Floor was, the higher was the average Tier on that Floor, mainly because of the better conditions and mana density and other things.
Around the 8th to 15th Floors is average Tier the Steel-Tier and some Bronze-Tiers, of course, this didn't mean that other ones wouldn't present.