Sorry for being so blunt, but this question is pointless unless you know what kind of style guide is relevant in your situation.
E.g., APA doesn't allow the use of ff. (see comments section):
http://blog.apastyle.org/apastyle/2015/03/when-and-how-to-in...Et seq. does work, but its use is being discouraged by people such as Ken Adams (
http://www.adamsdrafting.com/et-seq/ ) and Bryan Garner (see "Garner's Dictionary of Legal Usage").
Typically, you specify page ranges; "u.f." and "ff." don't tell you much.
Here are other abbreviations that all have the same meaning, basically:
http://abkuerzungen.woxikon.de/abkuerzung/folgende.phpBest
peer agreement (net): +4