Ah the age old commission split question. Here are some thoughts for you to chew on. When you start out in Real Estate you are pretty green and really need to focus on getting experience and building your brand. Going with one of the traditional brokers you'll most likely start out at a 50/50 split. It may seem low but you typically get a lot of training and mentoring that goes along with it. Its also good to join a brokerage with lots of agents that you can work with. It may seem like competition is a bad thing but in actuality if you join up with an office with many top producers you have the ability to help them with open houses and can also get mentoring help on your first couple of deals.
As you start getting experience and start making more sales, these traditional brokers like C21, Coldwell, etc... will give you better splits. As an experienced agent I've been offered 70/30 up to 90/10 depending on the volume.
You can always go with a 100% commission broker and only pay a per transaction fee. You get to keep most of your commission and you have the greatest amount of flexibility. The con obviously is don't expect anyone to hold your hand at this stage.
Hope that helps in your decision. I've always suggested to new agents to go with an experienced brokerage that offers maximum training and mentoring opportunities to help kick start your career. Once you have experience under your belt you can always hang your license somewhere else...or become a broker yourself!
Good luck!