HB dovetails on 1/2" drawer stock would require the 18 degree cutter.
You can't use the 12 degree on 1/2" stock because the depth of cut is
1/2", the same as the thickness of the wood. In such a case, the
cutter would go all the way through, and your dovetails would no longer
be half-blind. You'll want to use a cutter whose depth is at least
1/8" less than the thickness of you stock. On 3/4" stock, you'd use a
cutter with a depth of 5/8" or less, so you could use anything in the
10 to 18 degree range.
For this reason, the 18 degree cutter is the most versatile, since it
can be used with pretty much any thickness (as long as it's more than
1/2"). If you have thick stock, you can use the shallow high-angle
cutters, but the low-angle deeper cutters will give you stronger and
larger dovetails. Plus, dovetails are often used as much for their
looks as for their strength. Larger dovetails are easier to show off.