I have noticed that I feel much more mentally sharp after doing an hour of moderate exercise in the morning. On the contrary, when I meditate, I feel no such difference in my mental alertness. Isn't meditation supposed to improve working memory?
Focused attention meditation practices improve focus in the long term. So the improvement is difficult to asses and could probably only be found in a standardized test setting. Physical exercise however has been demonstrated to improve mental abilities in the short term (after recovery of physical exercise) levels of circulating neurotransmitter stay elevated for approx. 48h.
http://online.liebertpub.com/doi/abs/10.1089/acm.2007.7022 (Meditation and focused attention)
http://www.sciencedirect.com/science/article/pii/S0001691802001348 (Physical exercise and cognition)