What bird should I purchase?

I am interested in purchasing a pet bird. I have been researching for about one month and have narrowed down the possibilities to an african gray, sun conure, caiques, or a cockatiel. I would appreciated any input that any of you may have as to which one would be the best for me as a new bird owner. I work a normal 5 day week, however, don't want a bird that I have to spend all my off time with. Thanks for your help in advance.

Scott