The three plans are likely 401(k), 457, and 403(b).
Most employers who offer multiple options have a primary option, in your case, it's likely to be the 401(k), since they [employer] match contributions. Employer-matched contributions should be considered first (until you reach the max matching value) since that is "free" money.
All three are tax-deferred financial tools and have specific contribution limitations, withdrawal requirements, etc. Human Resources typically has specialists who can provide specifics of each. Contacting a Certified Financial Planner would also be in order to ensure the strategy you choose is a best fit for your financial situation and needs.
Also, I'm kinda old school, and while retirement planning is absolutely necessary and critical to begin now, I also believe eliminating debt is of equal importance. For example, contributing to a retirement account yielding 6% returns while maintaining debt balances charging 8% or more doesn't make sense to me. There's a balance there and everyone's tolerance and specific financial needs are unique.
Perhaps this video will help.