This is quite an interesting topic and one I watch closely.
I am a Leo and my soon to be fiancé is an Aries. So from a personal perspective I would say both are leaders but have very unique ways of leadership. So its quite hard to generalise who is a leader overall.
For example, I see the bigger picture that my Mrs perhaps doesn't. She was never one to plan, and I introduced her to planning. Now she sees the benefits of planning. I am probably not as spontaneous as her and she has shown me the value to being spontaneous.
Both of us are capable of leading, however my Mrs is more of a people pleaser than I am so most of the times she is more likely to go along with things. But saying that when she gets a bee in her bonnet about something she is very organised, practical and delivers.
This is one of the things that attracted me to her, if she has a task to do she achieves it.
In her worklife she is a true leader and possesses the skills to become successful. Me on the otherhand can be the same but I take a more relaxed approach. So its a hard call to make overall.