Trencher would be my first choice - assuming trench is wide enough. Excavator or backhoe excels if you need to go deep, or move large rocks. ...but slow and lots of work swinging side to side to dump each bucket.
I have used an excavato but not to dig a trench, I have watched a guy with a tractor and a backhoe attachment dig me a 5' trench (he did 300 feet in 1 day IIRC), and I have had friends use trenchers, but I have no further data on that. Also dug a 4' deep trench by hand Don't :P