Like someone said 'simple is best', and maybe simplify something is one of the hardest work like the mondrian's tree progression. Please kindly check out the following, it may be helpful for you to choose a good designer:

1. A designer who will really care about the core and philosophy of the logo
(not just concentrating in the appearance).

2. A designer who has great knowledge on typography.

3. A designer who will constantly trying to make it better and better than before.

4. A designer who prefers the two way-communication(not just waiting for your rate).

If you find someone with these conditions, congratulations.
You just found him.