27XL Ink

Same fit across all six printers, more ink in the XL. On machines like these, which are usually bought because someone prints a lot, the XL is the obvious choice on cost per page alone.

Yes, for the black. Epson produced a 27XXL black for some models in this family that holds more ink again than the XL, while the colours remain XL. Check whether your specific model accepts it before ordering, as not all of them do.

Yes. Black is a separate cartridge and can be ordered by itself. On a document-heavy machine it is the one that empties first by a wide margin, so most people end up buying more blacks than colours.

Nine times out of ten it is the chip. Remove the cartridge, wipe the copper contact with a dry lint-free cloth, and refit it until it clicks home. If the message persists, switch off at the mains for a minute and let the printer re-read all four slots.