If you are struggling in Alg2, talk to your teacher ASAP. Alg2 provides the foundation for Calc/PreCalc and even science classes. Try Khan Academy–their videos and practice can be very helpful. Try studying for 20 minutes a night, and write down questions you have about the material to look up or ask your teacher. Start creating good study habits now. The first half of Algebra II is basically a review of Algebra 1 skills (but more advanced), and then the second semester goes into newer stuff like logarithms, trigonometric functions, complex numbers, etc.
And to answer your question, the quadratic formula is quite tedious. Personally, I hate having to use it. Those other methods may be easier and quicker than using the quadratic formula.