citations - Choosing which version of an article to cite

I sometimes find an article published in several conferences.

If similar material is published in different conference proceedings, how do I choose which one to cite?

Answer

Normally you should cite the most recent version, which is probably also the most prestigious venue (normally republication is done while ideas are working their way up the prestige ladder). It's possible that only the earlier version contains the material you want to cite though, but unless that's substantially longer than a later version, then I would assume that means the author(s) have recanted that part, and you should probably mention that in your article e.g. "Bryson (1986) claims fish can fly (p. 253), though note later work does not reiterate this claim (Bryson 1991; Bryson 1993)."