All things being equal, it is better to use 12/3. You have no use for the
neutral (the white wire) now, but some day you might, and it is no harder to
run 12/3 than 12/2. It gives you the option of having 120v for a light or
something if you need it. I ran 12/2 and regret it.
However, if you run 12/2, Grizzly is correct. Just use the two insulated
conductors as your hots, no neutral needed.
I haven't grounded my "vacuum" lines, but some people do.
Are you sure the tools take 20a at 240v? What are they, 4hp?!