I've used the Life and Rexall brands with no problems, myself. I seem to recall seeing a post somewhere that confirmed that glycerin from RW Packaging (e.g. Life or Rexall) was vegetable-sourced. Perhaps in that Life Brand glycerin
thread linked above, even. Perhaps I just dreamed it.
Now, I'm not a chemist by any stretch, but glycerin from any source, if it's of USP purity, should be 99.5% (or whatever the
threshold is) C3H8O3, if I'm thinking this
through correctly. That said (moral concerns such as veganism aside), should it matter what the source is? I mean, glycerin is glycerin is glycerin, if it's pure enough, isn't it?
Unless that 0.5% of impurities is enough to drastically alter the character of the final product, of course. Just a thought.