PTFE (I think I got the letters in the right order) paste is best to use on hydraulic stuff. With the tape, you can end up with little pieces of the tape circulating around in the system just looking for an orifice to clog up. Use just enough to do the job... you don't need to douche the entire threads in the stuff.
Of course, this is assuming you're talking about NPT fittings. If your quick couplers are ORFS or ORB then you don't use any thread sealer. The quick couplers on my loader are ORB.