Lemmios - Link opens in app. Everything looks and works great EXCEPT Spoilers.
Mlem - Link opens in browser, not app. Manually went to test post. As with Lemmios, everything looks and works great EXCEPT spoilers.
Remmel - Instant fail. No development in 2 years, unable to even add an instance or an account. Non-starter.
Thunder - Hard to test. Lots of lag for some reason. Link opens in browser, not app. Manually went to test post. That being said, EVERYTHING worked. The lag may have been because I had just linked my account. Testing everything above, then coming back to Thunder, I found it fast and responsive.
Voyager - Link opens in app. EVERYTHING worked. No notes.
So, ranking them:
Voyager - EVERYTHING worked. No notes.
Thunder - Everything worked, but laggy to start with when using a year old account with lots of data. Once it caught up, everything was fine. Would probably be great with a new account.
Lemmios - Link opens in app by default. Spoilers don’t work.
Mlem - Link opens in browser by default but is user configurable. Spoilers don’t work.
Arctic - A few minor failures.
Avelon - A few more failures than Arctic.
Bean - Hey, it works better than Remmel. Probably abandoned.