None of those. Personal recommendations will always deliver above any automated solutions. Start with anyone you know who knows Obj-C, if you are posting this

None of those. Personal recommendations will always deliver above any automated solutions. Start with anyone you know who knows Obj-C, if you are posting this you probably don't know anyone that fits though. So the next step is to talk to anyone else in a similar business to yours and see if they have someone they have used and would recommend. The last step, post to places like HN asking for recommendations - if someone is willing to publicly endorse someone chances are they really believe in them.