When solving two simultaneous equations, when should you use the method of elimination and when would you use the method of substitution?

I would first always label the two equations as equation 1 equation 2. I would then look to see if you can cancel one of the variables out by adding or subtracting the two equations together. If this is possible then I'd use the method of elimination to determine the unknowns.
However, if one of the equations has a singular variable of x or y, that isn't multiplied by a factor. It would be easier to rearrange to make that variable the subject of the formula and then substitute it into the other equation then go ahead and determine the unknowns.