All-in-one printes can handle multiple functions  - printing/incoming fax, scanning/outgoing fax, or copying, and are ideal buys if you have average needs of these fucntions (not heavy duty need of one particular function).
The features to look for in all-in-one printers: Automatic document feeder that lets you put in multiple pages for scanning at one go. Auto-duplexing, which lets you scan, copy, or fax both sides of a document without having to intervene manually.

The best all-in-one printer in the market: HP OfficeJet Pro 8620 e-All-in-One Printer (heavy duty, value for money, reasonable enough ink cost per page.)
The second best all-in-one printer: HP ENVY 7640 e-All-in-One Printer (entry-level all-in-one printer, low-volume output)
The best upgrade to all-in-one printer: Epson WorkForce Pro WF-4630 All-in-One Printer (high-volume printing, so-so image quality)