digitalman
It's difficult to compare probiotics while their compositions and purpose vary quite enormously.
I can only talk about the ones that were tested on me via biofeedback:
Primal defense had many beneficial strains and are more transient in nature, serving more to mop up residue in the intestinal track.
Threelac was suprisingly one of the best for me for quite a while, likely due to having strains that feed on fungus (which seems to be in excess in my gut). I was tested yesterday and no longer seem to benefit from threelac.
Most acidophilus/bifidum type probiotics appear to be no good for my gut, they never tested well (these are the majority of probiotics outthere).
By far the most beneficial strain that has been consistently tested well is lactobacillus sporogenes. Perhaps its due to their remarkable stomach acid resistance, but these babies have highest implant rates of all probiotics.
Mike