This isn't even a contest

Both amazing actors, great men, and the epitome of manliness, but the only way one could deem Eastwood greater than the Duke is if they haven't experienced his work. Don't get me wrong, I'm a huge fan of Clint Eastwood and virtually all of his work, and I'll watch anything the man creates (Invictus, anyone?), but John Wayne was so awesome he could eat a handful of nails and defecate a complete barbed-wire fence without flinching.
If you voted for Clint Eastwood, go watch some John Wayne movies. Do it.
Do it. Do it. Do it. All glory to the hypnotoad.