I'm on Mastodon and I have both an iPhone and an iPad, so of course I've poked at a number of iOS clients for Mastodon. (I'm restricting my views to Mastodon specifically instead of the Fediverse as a whole because I've never used any of these clients on a non-Mastodon instance.)

I'll put my UI biases up front; what I want is basically Tweetbot for Mastodon. I think that Twitter and Mastodon are pretty similar environments, and Tweetbot has a very well polished interface and UI that works quite well. Pointless departures from the Tweetbot experience irritate me, especially if they also waste some of the limited screen space. Also, I can't say that I've tried out absolutely every iOS Mastodon client.

• Amaroq is a perfectly good straightforward iPhone Mastodon client that delivers the basic timeline experience that you'd want, and it's free. Unfortunately it's iPhone only. It's not updated all that often so it's not going to be up to date on the latest Mastodon features. As far as I know it only has one colour scheme, white on black (or dark blue, I'm not sure).

• Tootdon is also a perfectly good straightforward Mastodon client, and unlike Amaroq it works on iPads too. It's free, but it has the drawback that it sends a copy of toots it sees off to its server, where they are (or were) only kept for a month and only used for searches. The Tootdon privacy policy is written in Japanese.

  My memory is that I found Tootdon not as nice as Amaroq on my iPhone, when I was still using both clients.

• Toot! is the best iPad client that I've found and is pretty good on the iPhone too. It has all of the features you'd expect and a number of little conveniences (such as inlining partial content from a lot of links, which is handy when people I follow keep linking to Twitter; actually visiting Twitter links is a giant pain on a phone, entirely due to how Twitter acts). It's a paid client but, like Tweetbot, I don't regret spending the money.

  Toot! is not perfect on an iPad because it insists on wasting a bit too much space on its sidebar; you can see this in its iPad screen shots. It has a public issue tracker, so perhaps I should raise this grump there.

• Mast is written by an enthusiastic and energetic programmer with many ideas, which very much shows in the end result. Some people like it a great deal and consider it the best designed iOS client. I think it's a good iPhone client but not particularly great on an iPad, where it wastes too much space all of the time and has UI elements that don't seem to work very well. It's a paid client too.

  (Mast has had several iterations of its UI on the iPad. As I write this, the current UI squeezes the actual toots into a narrow column in order to display at least one other column that I care much less about.)

  I find that Mast is a somewhat alarming client to use, because it has so many features that touching and moving my finger almost anywhere can start to do something. So far I haven't accidentally re-tooted something or the like, but it feels like it's only a matter of time. I really wish there was a way to get Mast to basically calm down.

I think that Mast and Toot! are very close to each other on the iPhone; there are some days where I prefer one and other days when I like the other better. On my iPad it is no contest; the only client I use there is Toot!, because I decided that I wasn't willing to put up with what Tootdon was doing (partly because I wasn't willing to be responsible for sending other people's toots off to some server somewhere under unclear policies).

Both Toot! and Mast have a black on white colour scheme, among others. Mast has many, many customizations and options; Toot! has a moderate amount that cover the important things.

(I have both Mast and Toot! because I bought Mast first based on some people's enthusiastic praise for it, then wound up feeling sufficiently dissatisfied with it on my iPad that I was willing to buy another client.)

PS: I have no opinion on Linux clients; so far I just use the website. This works well at the moment because my Mastodon timeline is low traffic and there's no point in checking it very often.

(The problem with visiting Twitter links in a phone browser is that Twitter keeps popping up interstitial dialogs that try to get me to log in and run a client. Roughly every other time I follow a Twitter link something gets shoved in the way and I have to dismiss it. Needless to say, I hate playing popup roulette when I follow links.)