I chose to go to work for a non-competing broker because I thought she would be able to devote more time to training me--and I needed a lot! The competing broker I talked to had, at that time, about 50% of his office's listings (14 agents). He was so busy competing with them, I felt like I'd be taking up his time and he'd be taking away my potential work.
I have never regretted chosing a broker whose concern was for my career. She is the best!