I think Aikido, (at least Yoshinkan; i dont know how other styles train) is the best martial art to start out with because it teaches you two important things:
1. Body basics: we learn how to remain in a stable posture and use our power (not muscle power) properly. ex. lowering your hips, center line, hip power. We learn the proper way to move so we can maximize this power.
2. Aikido is about co-operation and respect for your opponent. It teaches us the best way to train so we can learn from one another.