<p>I have one table that saves comments for a varied set of content types. These are saved in other tables (news, articles, users). 
I wonder what's the best way to connect these tables?
In previous projects I used a second table for each kind of content. They held the id of the certain content mapped to ids of the comments table. So for each comment I had the comment entry itself and a 'connector' entry.
An alternative would be to use a separate comments table for any kind of content.
At the end both ways contain some redundancy flaw.</p>

<p>So which one should I use or is there the ONE solution?</p>

I would probably have a separate comments table for each content table so that I could take advantage of the foreign key relationships to automatically manage updates/deletes when the original content is changed/deleted.  So if I had news and articles tables, then I would have news_comments and article_comments tables.  Each of these would have a content_id field and a user_id field.  The content_id field would refer back to the content table and user_id field would refer back to the users table.  I'd set up foreign key relationships between the appropriate content and comment table and the users and each comment table and have the changes propagate on update/delete.  You might also want to set up indices on the id fields so that you are doing index joins between them.
If you have a single comments table, you would have to manage the relationships manually in code rather than having the DB handle it for you -- since you can only have the FK relate to  one other table.