The short answer is "not a lot of difference". The long answer is that the L tines on my JD 660 seem to do a better job when your tilling very shallow over the C shaped tines on my rotomec. When I'm tilling very deep it seems like the JD needs a bit more power relative to the Rotomec's C tines. I would get the kind that came on your Howard.
If your using L tines and its lugging the engine more than you would like get the C tines. If your into shallow cultivation for weed control get the L Tines. Either will do the job of the other however.