I use both and they give me different things. My wet ones (Infusium and Mizani ThermElastic) are for strength and elasticity (I also use Biolage Leave-In Tonic, but moreso for moisture.)
My creamy ones (NTM, Kiehls w/Silk Groom, Breakfree, Headress, Split End Mender, Keracare Leave-In, and the list goes on and on) are for moisture and, like Dolce Dawn said, instant gratification ('cuz nothing beats a good leave-in! Our leave-ins are the foundation of all styling, airdrying, etc.