Comparing ion qubits in the context of the surface code

Which qubit is better: A qubit that is sensistive to magnetic field fluctuations, but has no leakage states, or a qubit that is insensitive to magnetic field fluctuations, but can leak outside of the qubit levels during gates?  We answer this question in the context of Zeeman and hyperfine qubits of ytterbium ions in a surface electrode trap. N.C. Brown and K. R. Brown, arXiv:1803.0235