I'm currently testing Rodent for Mastodon, usually I use Tusky.
On desktop I use web, rarely any desktop application, I tried a few and Whalebird and Sengi looks good to me.
Until now I wasn't using any mobile app for Lemmy, and now I am testing Boost, Voyager, Connect, Summit and Jerboa.
That's all for Android, whatever I like for droid I can't have on iPhone, so I am currently not having anything installed on iOS.
What do you use for Mastodon and Lemmy, and what other interesting Fedi apps you tried so far?