Dino is slim and has some decent features, but Gajim is the client you want to be using today. Gajim has (although mostly broken) Voice and Video support as well as (working) plugin support and various plugins that you may expect.
Dino really fell short for me in my needs for XMPP client, though I'm happy to see federated systems and their clients being promoted.
Specifically Dino has issues with OMEMO support with Conversations, while Gajim does not see these issues. This means I can use Gajim on my computer and Conversations on my phone without issues.
We fixed some issues with OMEMO in the last months, so if your experience is a little bit older, those might be fixed already. If not, please report.
Dino has a very limited plugin system, extending it is planned for future releases. We are also interested in adding support for A/V calling and we already have some pieces of code for it, though nothing in a quality for actual usage.
As you said: Gajim does lots and lots of things, some of it only half-works. Gajim might be good for some people, but confusing for others. I probably wouldn't recommend it to my mom.
Dino has a good feature set and the user interface feels nice. It doesn't do everything, but that can also be a positive thing.
Dino's OMEMO works fine for me.
Gajim's an unstable mess that half of the time is not even connected to the server because it did not manage to reconnect after resume, or it just crashes.
It is fairly useless on dark theme, rendering grey on grey for the backlog.
Apart from a missing status notifier / appindicator, gajim is miles ahead.
What issues did you have? I used Dino and Conversations for six months or so a year ago, and enjoyed the experience. Our conversations were all OMEMO encrypted.
Dino really fell short for me in my needs for XMPP client, though I'm happy to see federated systems and their clients being promoted.
Specifically Dino has issues with OMEMO support with Conversations, while Gajim does not see these issues. This means I can use Gajim on my computer and Conversations on my phone without issues.