FLEXIcontent (FC) is one of the best, if not the best, CCK for Joomla! out there.
I've tested other CCK which can have a pretty interface but limites you in the free version; or others that can be so powerful that it's overwhelming to work with as there is too much to do.
And with many of these CCK, it's a pain to move your data out of them.
FC has multi language support with out the need of any 3rd party. You can map items (articles ...) to their translated version.
You can build almost any type of website with it. You have a vast array of field type.
You can manage the fields showing in the submit content form on the front end.
Tight and extended Joomla! ACL integration. You can even apply Joomla! ACL per field.
You can trigger SQL queries in field.
Drag & drop ordering.
The template system is uber simple and offer total control.
Maybe not every developer or company are great at advertising themselves. But there is one sure thing about FLEXIcontent: it's a solid CCK.
And i forgot one important note: It's FREE!
ps: i'm not even part the of the FC team, but i simply love it. We use it a lot to develop our client's website.