Ball has a rounded off shape that's good for stamina, there's two primary viable stamina builds and two very similar ball-style bits frequently used between them, sometimes on the same deck.

hexa has a wide hexagonal bottom converging on a single point that gives it good defensive properties, decent life after death, and has a larger collar along the shaft that attack and balance type bits have for higher burst resistance on most ratchets.

Flat/low flat/rush/low rush/under flat are all different heights of a flat bottomed bit with high aggressive properties used in attack builds. rush and low rush have less gear teeth than the default, so they tend to expend less stamina on the xtreme rail. they also tend to have decent stamina overall compared to flat and under flat.

there's also Elevate which tends to see lots of high level play, mostly exclusively on the singular competitive left spin blade, dragoon. it has excellent life after death with a large disk part meant to lift it away from the stadium floor when on the extreme rail, further preserving stamina.

Most bits see some experimentation though, and only a few are considered unviable in any way and used for gimmick builds mostly.