A lot depends on just how smooth you want it. What are you going to mow it with. If you plan on mowing it with your tractor or a riding mower, it doesn't have to be as good as if you are getting a ZTR. ZTR's go sooo fast that you want it as smooth as possible. And it doesnt have to be perfectly flat either. gently rolling is still smooth to mow with whatever you use.
That said, I wouldn't want to use the tiller. It will take forever IMO and tilling hard ground is rough. And unless you plan on gardening as well, a tiller is going to be expensive for this one time thing.
I would use a box blade and run the rippers all the way down and toplink as short as possible. This will make the rippers dig the deepest. And I would look for a box blade that has as many rippers as you can get. This will break up the ground similar to what a tiller would do. Then raise the rippers and lengthen the toplink and use the boxblade like normal to move and distribute the dirt into the low spots. Then once "roughed in" go over it with a drag similar to what has been mentioned.
Another attachment that isn't too expensive if you shop c-list is a landscape rake. It will do a similar job as a drag, only it will gather a few more rocks and get them out of the yard for you. They do an excellent job for a finish grade if the soil is already broken up. Seed it and straw it. Then stay off of it until it hardens up or you will just rut it back up.