Comparing is slightly complicated but roughly speaking:

Difftastic only diffs code, which is only 2/3 of all diffs.

When only measured on stuff difftastic supports:

Difftastic is perfect on 64% of diffs and near-perfect on 17% more.

Omnidiff is perfect on 90% of diffs and near-perfect on 5% more.

Speed is

p50 - 35ms difftastic vs 4ms OmniDiff p99 - 637ms vs 420ms

Difftastic wins on license. MIT vs AGPL.