I couldn't get a good fit, good comfort, and good isolation from any of the factory Shure tips (some gave me two out of the three but I was adamant that I needed the trifecta). Fortunately this was one of those problems that could be solved just by throwing money at it, and ~$200 later, Sensaphonics custom silicone tips gave me what I was looking for.
Etymotic and Shure seem to give the best isolation, and Sensaphonics can make custom tips for both. (I don't especially recommend ACS Custom which was long the 'factory approved' supplier for Etymotic.)
Comply Foam makes memory foam eartips which give isolation equal or very,very close to the customs and you can buy years' worth for the cost of customs. They work well on my Ety's but or the Shures, only the customs gave me all that I wanted.