I like a simple spade; long or short handled depending on the angle you're working at. I've developed a technique of cutting out one row of sod with a grub axe where the mound will be placed. I flip the sod over and that's the base for the swale mound. Moving uphill from there, I use the spade to remove soil and sod together. This material is flipped "sod side down" and piled on the mound base. Repeat the process until you've completed the first pass for the width of the swale. That leaves the sod layers with soil in between at the bottom of the mound. From there make a second pass to deepen the swale. This material has little biomass and less seeds but it makes a nice barrier to the sod creeping back to the surface. I chuck a good layer of
compost on top of that and then mulch. Seed or add
trees and other transplants and you're off and running.
This a method that just requires you to find a good methodology that works ergonomically for you. I was able to do a couple hundred feet of swales in just a couple sessions once I figured out what worked for me. Doing a lot of swinging of heavy tools can be rough on your upper body. By incorporating multiple tools and body motions you'll save a back ache and sore arms. I've found it easier to use my feet and legs to use a spade to cut into the soil and then using my back and legs to toss it onto the mound.
Also, have a gravel rake and a leaf rake handy to do the finishing touches. Neatness counts
Not really
Good luck and don't forget to post pictures