The larger firms will be pulling the most business. Though it is true that you will likely not be handed any deals, you do get exposed very quickly to the fast pace of the business. You could be handed some prospective listings to work. They will not be easy ones, as the other brokers will have picked over them. But, just having the firm name behind you and a good attitude and approach could get you a listing more quickly in the larger firm.
The smaller firm may not be able to feed you as many listing opportunities, but many new commercial agents have found that better quality training is available in the smaller firm. The larger firms may have training programs, but they may not take the time and effort to develop your specific talents. Rather, you're placed into a fast-track program with little support along the way. This isn't always the case, but take care to question the management or owners of the firm about training and who you can call on for advice and help.
Will mentoring be offered? Some larger firms structure it into their training programs, and there is a cost somewhere. Be sure you understand how the mentor is compensated so you will not have a big surprise when you get your first commission check. Sometimes a smaller firm can provide mentoring that is less structured but not costly either. The owner or management will work with you without taking any of your commission in some cases. They invest in your growth, hoping to see a return down the road. It may be more difficult to get this position, as they will want to see probable future rewards from the time and effort that will be expended on your training.
There isn't an easy answer to the small or large firm size question. It is up to you to interview them as much as they do you. See how their training and career development goals mesh with yours. Don't make a decision based mainly on how fast you'll get a commission.

