It depends on which you are more comfortable with. Neither is "best" for all situations.
Some people prefer dealing with someone local, someone they can get in touch with by a phone call or an office visit.
Some people prefer dealing with people online, someone they can easily reach by email and communicate in their free time.
Whether you hire someone local or on the internet, the possibility exists of them stealing your designs.
That goes back to dealing with someone you are comfortable with. You need to use your gut and vet each designer you are considering so that you are comfortable sending your ideas to them.
It's not really in a designers best interest to steal a design. You don't get many repeat customers that way.
Sure, there are shady people out there, but it's not the norm. You just need to do your best to vet them out and avoid them. Check references, etc.
But don't let fear of getting your designs stolen keep you from moving forward.
As soon as you start selling, the world will see your designs, and if they want to steal them, they might. All you can do is try your best to protect them, research copyrights/trademarks (see the Resources area to the right or search the forums), and decide whether or not how or if you want to pursue people that take your intellectual property.