Not sure which to purchase.
The only published extra feature for mfc-8870dw is wireless WIFI, according to Brother's website. We don't need or currently use WIFI.

The MFC-8870 was released in 2007, the MFC-8860 in 2006.
Sometimes a mfr will slipstream improvements in later models, more recent electronics, lower power. Sometimes not.

If you have used both models, have you noticed any other differences besides the Wireless WIFI?