I have been using Mammoth, since it was in TestFlight, but weirdly I feel like following the official release it has gotten progressively more buggy and unstable so I’ve been resorting to the Mastodon App more and more lately. But I can’t find a way to post GIFs in that, so I’m currently sort of jumping around between Mastodon’s App, Mammoth and Metatext for posting GIFs.