I've been using ProBiotics for years.  The best is a strain called DDS1 and
it's only usually available at the Health Food Store.

Acidophilus is a bacteria and therefore should always be kept cold.  Buy it
IN the cold section and keep it in the fridge or the little critters die.

I order it directly from a Company but they still guarantee the potency
even after shipping.

There is a HUGE difference between brands.

Love,

Amy