  Recently, West and Fong [New J. Phys. 14, 083002 (2012)] introduced an echo
scheme for an exchange-only qubit, which relies entirely on the
exchange-interaction. Here, we compare two different exchange-based sequences
and two optimization strategies, Uhrig dynamical decoupling (UDD) and optimized
filter function dynamical decoupling (OFDD), which were introduced for a
single-spin qubit and are applied in this paper to the three-spin exchange-only
qubit. The calculation shows that the adaption of the optimization concepts can
be achieved by straight-forward calculation. We consider two types of noise
spectra, Lorentzian and Ohmic noise. For both spectra, the results reveal a
slight dependence of the performance on the choice of the echo sequence.
