The IRS requires that you use your W-2 ... it is not an option. Using the LES increases your chances of messing up your return which will require an amendment that takes 16+ weeks to process. And read this tidbit on refund delays this tax season ...
https://www.irs.gov/for-tax-pros/new-federal-tax-law-may-affect-some-refunds-filed-in-early-2017
And since you will get your W-2 before the IRS is ready you really have no reason to not comply with the rules.
See the release dates for the DFAS W-2's here : http://www.dfas.mil/
