A ten-second decision

1. Get it in standard form ($= 0$).
2. Every term shares a factor (or $c = 0$)? Take out the GCF.
3. No $x$ term ($b = 0$)? Square roots: isolate $x^2$, then $\pm$ (negative → $\pm$ imaginary). $x^2 - 81$ also works as a difference of squares.
4. Otherwise find $b^2 - 4ac$: a perfect square → factor; not → Quadratic Formula.

The formula always works — factoring is just faster when it's available.