I've already talked about this at length in the Feb 2020 Monthly Showcase, but my vote is Ozzy & Strut, if anything, because with the TV series' focus on Chomper, it would have been thematically appropriate for the eggstealer duo to run afoul of the egg who eluded them all those years ago.
It might even make for an interesting arc where Chomper has to stave off a desire for comeuppance given his friendly sharptooth status, especially since Ozzy had tried to have him killed for a snack in LBT2. If Ozzy and Strut had made an appearance things would have come full circle, given the gang's friendship with Chomper only happened because of the eggstealers' interference in the valley, and I just think that it would be a nice finale to wrap things up thematically for Chomper.