Stop valve vs. Gate valve vs. Ball valve: Who’s the winner?
There are three basic valve styles, making this a classic case of good, better and best (described in order as follows). All three can be used for water, oil or airflow control if the casting has "WOG" stamped on it.
Stop valves are closed by screwing a rubber gasket down onto a seat in the middle of the valve. Pros only use small versions that act as shutoff valves for fixtures such as sinks and toilets and outdoor sillcocks. Flow is inefficient because of the circuitous route the fluid (water, in most cases) has to follow. It's important to orient the valve in the right direction with the arrow (cast into the side of the valve) aligned with flow direction. That way, water flows against the bottom of the rubber gasket. If the valve is put in backward, the flow will force the gasket away from the top of the valve.
Gate valves are called "full-flow" valves; there's a direct unobstructed path for flow right through the middle of the valve. A wedge-shaped brass gate is lowered into a machined slot to close the valve. They should either be completely open or completely closed. Water flowing through a partially open gate valve wears away the metal and causes the valve to fail over time.
Ball valves contain a finely machined stainless steel ball with a hole drilled through the center that pivots in plastic bushings. Like the gate valve, it's a full-flow valve. The hard steel allows this valve to be partially open without wearing out. In the closed position, the lever is perpendicular to the pipes; in the open position it’s parallel, so a glance will tell you if it's open or not. The downside? If the pipes are tight against the wall, you may not be able to operate the lever.