System Of Equations
The best time to use graphing is when you have two equations that are both in slope intercept form. For example, y=2x+3 and y=-2x-3.
The best time to use substitution is when one equation is in slope intercept form and the other in any other form. For example, y=2x-4 and 3x+2y=4.
The best time to use elimination is when both equations are in the same form and have one variable in common. For example, 2x+5y=10 and -2x-3y=-14.