Which ink/toner does the Brother MFC-L5850DW use?

The Brother MFC-L5850DW (laser, 2016) uses TN-850, TN-880, TN-820.

Compatible cartridges

CartridgeColorYieldPagesOEM priceCost/page
TN-850 black XL8000 $110.00 1.4¢ OEM · AmazonCompatible
TN-880 black XXL12000 $160.00 1.3¢ OEM · AmazonCompatible
TN-820 black standard3000 $80.00 2.7¢ OEM · AmazonCompatible

XL/high-yield cartridges usually cost more upfront but lower the cost-per-page — better if you print often.