I was with another major broker in the Chicago area for over 12 years before joining Baird & Warner....about 2 1/2 years ago.
The reason I joined Baird & Warner was their reputation, internet presence, market presence, training, up-to-date technology and the overall feel of their offices. I believe it was a great business decision for me. I think I am able to offer my sellers/buyers great services when working with me.
I think you should interview several brokerages and make sure they fit with what you are looking for. Ask about training, buyer/seller services, internet marketing, their local market presence, etc.. Talk to agents that work in those offices, as well.