If this is an exercise from an introductory calculus course, one place students are going to need this skill is in applying the chain rule. The alternative composition you propose, as well as the alternative compositions in Steve's answer are not going to be very helpful in that context.
For the purposes of the chain rule, what is needed is a decomposition into simple functions, each of which the student knows how to differentiate. Since students usually learn rules for derivatives of polynomial functions, power functions, the logarithmic and exponential functions, and trigonometric functions, you could ask for a decomposition into only functions from that list. You need to make sure that students will recognize the square-root function as a power function (a skill that, again, will be required when it comes time to learn differentiation).