how big are the rocks and how big is the field? A rockhound does a great job but rocks bigger than 6" can damage the tooth bars or twist them.
If you have a lot of small rocks and can get a skid steer that can handle 2500lbs or more and take your time, a rockhound will leave the ground ready for seed. The attachment is heavy and you have to take your time or you could damage it but for the years I owned one, I never found another way of making an almost rock-free field.
It all depends on how big an area you want to clear, the size of the rocks, soil type. Also, do you have a tractor that you want to use for this purpose? There are a lot of methods available dependent upon equipment you have.