Gate and ball valves are normally meant to be in the full open or full closed position.
Neither is really meant to be used as a flow control valve - even though both can obviously be used for this purpose. However one can not be really considered "better" than the other for this purpose.
A full port ball valve has an opening in the ball the same size as the pipe. Normally harder to find and more expensive.
A standard ball valve has an opening one size smalller than the pipe.
There is also a reducer ball valve which has an opening 2 sizes smaller than the pipe - also harder to find and more expensive but the "better" choice if the point is to use it as a control valve.
Gate valves usually have an opening nearly the same size as the pipe (seat is like a channel the gate slides down) but are cheaper than a full port ball.
If a gate valve gate is a wedge shape it may will rattle when operated partially open and will wear the gate and seat to the point it will leak past the seal even when closed.
Hard to tell without disassembly if the gate is round or rectangular and wedged or planar. Sometimes you can look down the open end and watch the gate operate. It will be pretty obvious if the gate is wedge shaped.
A globe valve (or needle valve - more expensive and more precise) is preferred when throttling is required.
Globe valves are not normally recommended if full flow is required as the seat is smaller than the pipe and the fluid must go through multiple directional changes so these valves will and will always restrict flow even if fully opened.
Jeez, been over 30 years since the Navy taught me this stuff and it came back like yesterday. Hopefully the memories of 7 month Med cruises won't haunt my dreams.
