Yes, hardeners are different and they effect you in different ways; but they are all hazardous to your health. TDI (toluene di-isocyanate) used with Urethanes is one of the worst.
Whether you use hardeners or not, the paint itself is hazardous because in almost all paints the primary filler is Micro-Fine Silica. If you should inhale the paint dust it would be the same as inhaling microscopic razor-blades - can everyone say: SILICOSIS . It may not get you right away, but it will get you.