1) "In cellular biology, pinocytosis ("cell-drinking", "bulk-phase pinocytosis", "non-specific, non-adsorptive pinocytosis") is a form of endocytosis in which small particles are brought into the cell suspended within small vesicles which subsequently fuse with lysosomes to hydrolyze, or to break down, the particles. This process requires adenosine triphosphate (ATP), the chemical compound used as energy in a majority of cells. Pinocytosis is primarily used for the absorption of extracellular fluids (ECF), and in contrast to phagocytosis, generates very small vesicles. Unlike receptor-mediated endocytosis, pinocytosis is unspecific in the substances that it transports. The cell takes in surrounding fluids, including all solutes present. Pinocytosis also works as phagocytosis, the only difference is that phagocytosis is specific in the substances it transports. Phagocystosis actually engulfs whole food particles,which are later broken down by enzymes and absorbed into the cells. Pinocytosis, on the other hand, is when the cell engulfs already dissolved/broken down food. Non-specific, adsorptive pinocytosis is also called receptor-mediated endocytosis." Source: http://en.wikipedia.org/wiki/Pinocytosis 2) pinocytosis = "non-specific, non-adsorptive pinocytosis" "receptor-mediated endocytosis" = "non-specific, adsorptive pinocytosis" The only difference is that the second pinocytosis is adsorptive, and the first not. 3) here is the fonction and the advantages of the receptor-mediated endocytosis: "The function of receptor-mediated endocytosis is diverse. Obviously it is widely used for the specific uptake of certain substances required by the cell (examples are the uptake of LDL via the LDL receptor or iron via transferrin). The role of receptor-mediated endocytosis is also well recognized in the downregulation of transmembrane signal transduction. The activated receptor becomes internalised and is transported to late endosomes and lysosomes for degradation. However, receptor-mediated endocytosis is also actively implicated in transducing signals from the cell periphery to the nucleus. This became apparent by the finding the association and formation of specific signaling complexes is required for the effective signaling of hormones (e.g. EGF). Additionally it has been proposed that the directed transport of active signaling complexes to the nucleus might be required to enable signaling as random diffusion is too slow (Howe, 2005) and mechanisms permanently downregulating incoming signals are strong enough to shutdown signaling completely without additional signals transducing mechanisms (Kholodenko, 2003)." Source: http://en.wikipedia.org/wiki/Receptor-mediated_endocytosis

I don't know if you can call it more efficient, but it is definately more specific. Receptors recognize certain molecules and internalize them, while pinocytosis involves taking in a little bubble of the extracellular milleui and whatever comes in with it.