Look at Janome and also the sergers at Hancock Fabrics which are made by Janome. I have been using a Janome made Kenmore since 2006 and it has never given me a spot of trouble. I have loaned it out to a lady whose serger was in the shop and she loved it.
My serger is equivalent to the Janome 3434D. The next model up has lay in threading which is not easier or more difficult than the tension knobs to thread. The difference is appearance.