Sponge is more 1.8 forward…
That said, a lot of the ‘bypass’ that mods have done in the past won’t be as much of an issue IIRC with Sponge. Being as though both Sponge and Mods mostly use Forge, I think there won’t be the issue where the old server software would never see an action as it bypassed it.
Someone with more knowledge can clarify, if they like.