Both printers include colour printing, USB connectivity, and borderless printing. Their most relevant distinctions are ISO black print speed and automatic duplex printing.
DCP-T230 has ISO black print speed of 16 ipm, versus 10.5 ipm on ET-2856. ET-2856 supports automatic duplex printing, whereas DCP-T230 does not. ET-2856 supports Wi-Fi, whereas DCP-T230 does not. DCP-T230 has standard paper input capacity of 150 sheets, versus 100 sheets on ET-2856. DCP-T230 has black first-page-out time of 6.2 seconds, versus 10 seconds on ET-2856.
The paired specifications favour DCP-T230, particularly on ISO black print speed. The other model may fit better if its own strengths matter more to you. Consider the first model if ISO black print speed matters most; consider the second if automatic duplex printing is the priority.