MDPV for sure! And i don't really understand it, but i want it all te time if i don't have it, but isn't that enjoyable when using it. It is far more addictive than drugs i have used like d-amp, l-amp, meth, ritalin, mdma, opiates, benzos, weed, alcohol, nicotine, and all of the other 20 + research chemicals i have tried... Something is really strange about MDPV, it has to be something special about it since it's so different in the addictive way. I never really crash from it, no withdrawl, just the longing for more. Function well without it, but in my dreams i have my bag with me every night.