Jabber is an open protocol and anyone may develop a client for it. This means there are many different clients to connect to jabber.at.

So what's the best client?

Here is what we have found works best:

Can you be more specific?

Sure we can:
Client XEP Notes
0027 0167 0198 0280 0313 0352 0357 0363 OMEMO
Adium
ChatSecure
Conversations on Google play (€ 2,39), on F-Droid (free)
Converse.js
Gajim
Jitsi Good for voice/video calls
JSXC You have to host your own instance.
mcabber
Monal
Pidgin
poezio
Profanity
Swift
Xabber on Google play, on F-Droid
yaxim
Zom
Feel information on this page is missing or out of date? Please just contact us.

You can also find other lists of clients on xmpp.org, Wikipedia, on zash.se, or, in French, at jabberfr.org.