Are you hunting cottontails or big hares? If you're hunting big hares and can't get real close, I don't think big rubber blunts should be used. Cottontails are a different story.
I've used nutters, broadheads, hex heads, plain steel blunts, judos, and big rubber blunts. Where I hunt is also covered with lava rocks.
For cottontails, the big rubber blunts are my favorite. For one thing, your arrow is more likely to survive if/when you hit one of those rocks. I generally limit my shots to sitting head shots in a range where I feel confident that I can fairly consistently hit a lemon-sized target. I never aim for the body. A head shot with one of those big rubber blunts is almost always an instant kill.
My second favorite are nutters. However, if you hit anything hard, the nut always comes off it seems, and usually you can't find it. So I cut the arrows a little long, and carry a baggie of nuts in my pocket to replace ones that break off.