I must humbly disagree. Some brands of sustanon and some brands of straight prop hurt like hell, and others are totally painless. (truthfully iwanabe, you are the first person I have met who had any pain from Viramone. There are some fakes out there. Testovit is totally painless as well). Omna is a pain free sustanon.
I believe that the culprit is the benzl alcohol used to aid in suspending the molecule, and primarily as a preservative. Mexican gear is notorious for substituting alcohol for clean lab conditions. Even the enanth from certain companies hurts like hell.
Test suspensions made by compounding pharmacies are virtually alcohol free, painless, but only have a shelf life of a few months instead of a few years.
The crystalization issue occurs in water based suspensions. These are designed to form a crystal depot for rapid absorption, as opposed to the slower oil depots.
I was friendly with a fellow who worked at a pharm lab. Batches were tested for bacteria count. If the count was too high, they just added more benzl alcohol. You all know this product, and it hurts like hell.