Both printers include colour printing and USB connectivity. Their most relevant distinctions are fax and ISO black print speed.
ET-5850 offers print, scan, copy, and fax, versus print, scan, and copy on DCP-T230. ET-5850 has ISO black print speed of 25 ipm, versus 16 ipm on DCP-T230. ET-5850 supports an automatic document feeder (ADF), whereas DCP-T230 does not. ET-5850 supports automatic duplex printing, whereas DCP-T230 does not. ET-5850 supports automatic duplex scanning, whereas DCP-T230 does not.
The paired specifications favour ET-5850, particularly on fax. The other model may fit better if its own strengths matter more to you. Consider the first model if included black ink yield matters most; consider the second if fax is the priority.