  The time step criterion plays a crucial role in direct N-body codes. If not
chosen carefully, it will cause a secular drift in the energy error. Shared,
adaptive time step criteria commonly adopt the minimum pairwise time step,
which suffers from discontinuities in the time evolution of the time step. This
has a large impact on the functioning of time step symmetrisation algorithms.
We provide new demonstrations of previous findings that a smooth and weighted
average over all pairwise time steps in the N-body system, improves the level
of energy conservation. Furthermore, we compare the performance of 27 different
time step criteria, by considering 3 methods for weighting time steps and 9
symmetrisation methods. We present performance tests for strongly chaotic
few-body systems, including unstable triples, giant planets in a resonant
chain, and the current Solar System. We find that the harmonic symmetrisation
methods (methods A3 and B3 in our notation) are the most robust, in the sense
that the symmetrised time step remains close to the time step function.
Furthermore, based on our Solar System experiment, we find that our new
weighting method based on direct pairwise averaging (method W2 in our
notation), is slightly preferred over the other methods.
