This is a highly individualized question. What's best for you may not be best for anyone else in Chicago. Having just changed firms recently, I'd suggest looking at the following:
What geographic areas would you like to work in and what brokerages are active in that area?
If there are agents who are particularly successful in the geographies that you're considering, speak with them and get their opinions on both their current brokerage and other brokerages that they might consider (and ask them why they might consider a different brokerage). I'd consider trying to talk to as many different agents in a particular office as possible to get many different perspectives.
In addition to what commission split is offered on closed transactions, find out what the fee schedule is for other services offered by the brokerage. If you are planning to do a lot of direct mail marketing instead of internet based marketing, then you must know how much your anticipated costs will be to conduct your business at each brokerage that you're considering. This REQUIRES that you have some sort of business plan as you're beginning your real estate career.
Look at real estate ads (print and/or internet) out there and if there are companies whose marketing you've found to "speak to you" particularly effectively, then contact them first. If there is a consistency of presentation that you find yourself attracted to from multiple agents from a particular brokerage, then that might indicate somewhere you'd be comfortable hanging your license.
If you'd like to discuss further how I made my brokerage decision (either recently or when I first entered the business 5 years ago), I'd be happy to speak with you. Just call or email me at any time, and good luck to you.
Broker Associate, Sudler Sothebyâ€™s International Realty
1634 E. 53rd St. 2nd Floor Chicago, IL 60615
773-418-0640 (mobile) 312-577-0985 (fax)