HL-L5100DN and MX317dn share specifications such as Print Technology (Laser), Automatic Duplex Printing (Yes), USB (Yes), Ethernet (Yes).
The main differences: Printer Functions (HL-L5100DN: Print, MX317dn: Print, copy, color scan, network scan, fax); Black Print Speed A4 (HL-L5100DN: 42 ppm, MX317dn: 33 ppm); Print Resolution (HL-L5100DN: 1200 x 1200 dpi, MX317dn: 1200 x 1200; 2400 IQ (2400 x 600); 600 x 600; 1200 IQ (1200 x 600) dpi).
HL-L5100DN may suit users who need its differing values, while MX317dn benefits those who need its paired strengths. Review the specs table above before deciding.