Fedilab. It costs $2.99 to buy it, but it’s the best and most feature complete right now. Elk is a good client, but it’s web-based (and can be installed as a web app on mobile). But it still has a lot of soul searching to see if it’s trying to be the “Twitter client” of mastadon or not.

I use them both occasionally, and fedilab is my primary mastodon client right now for lots of reasons.