OG has a more intense heat sensation (HOT HOT HOT!) but I love it. Trying some Smolder now, and it seems to be as effective without an intense burn; but you still know its working!
I wouldn't advise it pre-sex, or any type of interaction that it can get rubbed off where it shouldn't; it is a topical cream, so its the same as any other type of cream that you wouldn't want to smear.
In terms of discoloration, I have gone through several of OG, and my first smolder now, with none at all. If you don't put on too much, it won't affect clothing either; but if you put it on, i have heard stories of it affecting white clothing, washing out easily.
I notice skin-tightening (I have gone from 283-173-210 currently) and loose skin has been an issue for me.