Both classes will help you gain strength and flexibility and will offer a lot of compliments to your running regiment. Yoga will give your body a completely balanced workout, which I think may be more beneficial in the long run. It depends exactly what you're looking for. I wrote this article a while ago and it outlines the benefits of both and differences between them. http://www.active.com/mindandbody/articles/Yoga_Versus_Pilates__Which_One_s_Right_for_You_.htm. Hope it helps!
ACTIVE is the leader in online event registrations from 5k running races and marathons to softball leagues and local events. ACTIVE also makes it easy to learn and prepare for all the things you love to do with expert resources, training plans and fitness calculators.