I have found in all of my printers (three, different brands) that the cartridges that come supplied with the printer far outlast replacement cartridges.
It has got to the stage where it is often cheaper to buy a new printer, with cartridges, than just the replacement cartridges.
This may not be the case with all makes of printer however.
Many thanks for your responses. Vehelpfulguy, thanks for the links but unfortunately I need the printer yesterday, have course work to hand in at college on Tues so have to go buy one today.