142s are used all over the place down with ATW. All over the Cardiff Valleys (Merthyr, Rhymney, Treherbert, Aberdare, Maesteg, Penarth and Barry Island) mainly, with some diagrams to Cheltenham Spa, very unusually on stopper services to/from Swansea and Cardiff Central, the City Line (Coryton - Cardiff Central - Ninian Park - Radyr) and the first service from Hereford and some Sunday diagrams on the Marches (usually when there's engineering works on as they never go north of Shrewsbury) and Hereford terminating services.
143s can, as said, work where the 142s do.