Depends on what your goals are. You can start looking around to see what teams there are in your area and start reaching out to meet with the team leaders. Your splits will usually be lower on a team but if they are productive you may get leads and training you wouldn't otherwise have easy access too. You can actually see and learn how a top producer runs their business and emulate that later down the road. However, you want to vet the team before signing on so you don't find yourself in a churn and burn situation or on a team that promises endless leads but in reality gives few or no leads but still expects a cut of the leads you generate yourself.
If a type of market is what you want to focus on, like luxury, small multi-family, starter homes, certain neighborhoods you know, etc., then you can start seeing what brokerage is dominating that area and start reaching out to those managers at that brokerage. This can be as simple as driving the areas you'd like to sell in and counting the signs you see in the yards and comparing. At the end of the day though, like Preston and Brandon said above, when you are starting out you will want to do your best to assess what brokerage can provide you the best training and support structure to get you up and running. Getting your first few sales can be quite difficult so finding someone who will guide you in that first year can be really beneficial, especially in this low inventory market. You can always jump to a different brokerage once you have learned the ropes. In fact, the more you sell, the easier it becomes and you may find brokerages will try to poach you to join their firm.
Also, start reading books now so you can start to decide on what lead generation activities might work for you. Books like The Millionaire Real Estate Agent by Gary Keller, Your 1st Year in Real Estate by Dirk Zeller, David Greene's agent book series, Ninja Selling by Larry Kendall, etc., are all good places to start.
Best of luck!