I have a New Home MyLock 4 thread with differential feed. I've had it for years & love it. Be sure you get one that has nothing in the way of threading the needles. I use mine for a variety of projects - rolled hems for napkins, with the blade disabled it makes a ruffled effect on sweatshirts and my favorite is an easy baby or child's quilt done in 6 inch strips where you sew together front, back & batting in one step & when it's finished you're done unless you want to bind it rather than serging the edges too.
Betty