I agree with everyone here. It depends on the two pair hand you were dealt and in what position. I read this in Hwang's plo book. If you are dealt a two pair hand in omaha, you will hit a set one out of 4 times. But the only problem here is the set you make. If you are playing the low two pair hand like 3388 and hit a set of three's, your chance of hitting a set over set is greater. You will lose alot of money with this hand. That is why most people will not play a two low pair hand preflop. AAKK is a great hand to play from all positions, but it will depend on your position and preflop action to you for you to decide if you want to raise it up.
3 of kind dealt to me is an instant muck. The only time I might consider it is if it is AAAK with the AK suited or if 8 or better, AAA2. Otherwise, I am waiting for future hands to play.
Scarby