Ballistic performance of graphene, silicene, and germanene-nanoribbon field-effect transistors (FETs) with a gate-length of 10 nm has been numerically investigated. The graphene-nanoribbon FET is found to have the largest ON-current when one compare FETs with a nanoribbon channel having a nearly equal band-gap E_g ≈ 0.5 eV. The graphene device exhibits the largest OFF-current due to the smallest effective-mass enhancing the source-drain direct tunneling.