Unfortunately I can't answer your specific question on recommending a brand of probiotic, as my work in this area hasn't been related to IBS.
In the course of other work however some part of it does have to do with IBS.
Briefly, the human gut microbiome normally has 1000 or more types of bacteria, in an amount such as 100 trillion cells. Relative to this, for example a product which provides say 6 types of bacteria in a total amount of say 10 billion CFU's (which pretty much is "cells") is pretty much a joke. Even if every single bacterium made its way safely into the intestines, they'd be outnumbered 10,000 to 1 by what's already there. At least if comparing on a total basis: if considering only the proximal small intestine, then the outnumbering would not be as bad. However even then we run into the issues that administered lactobacilli, for example, are found present for only about 3 hours. And basically, bacteria that are capable of colonizing the intestine will already be there, unless one has never been exposed to it before. As the probiotics are generally common bacteria, usually one will have been exposed before anyway. (Or when the probiotic is comprised of unusual bacteria, this tends to be with no evidence behind them and chosen apparently just because they're easily cultured and commercially available.)
However, despite these problems, IBS is one of the few things for which probiotics have shown benefit in some instances, more towards alleviating specific symptoms rather than generally overcoming the condition. A general review is here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3785618/
On specific products, I cannot now recall if I have read a reference on VSL#3 and IBS. I did read one about that product recently on a completely different subject, which is why it comes to mind now. At least the number of bacteria of that product is plausible.
Certainly part of the problem is adverse balance of bacteria. Agents reducing amounts of problem bacteria could be of as much help as introducing, usually transiently, some beneficial bacteria. One method is treatment with rifaximin: http://www.ncbi.nlm.nih.gov/pubmed/21208106