Cloth is recommended al pi kabbalah, however buttons are better al pi halacha. I think it depends if a frock is a beged shel kedusha or shel kavod. If it is a din in kedusha in separating am yisroel from goyim than cloth is preferable, since it is more distinct from levush goyim. If it is a din in kavod i.e. kovod shel torah or kovod lefnei hamokom, lhavdil like is seen by the nobel prize dinner or other upperclass events, than buttons may be preferable. As always one should ask his rebbe before he switches from one kind of frock to another. Eilu VeEilu Divrei Elokim Chayim.