August is bad. But if you want to make a choice Yam le Yam (Sea to Sea) is definitely a better choice. You have more shade than in other places. Nahal Amud on day 3 or 4 of Yam le Yam, is hot, very hot, because of the high cliffs above it, on both sides. Make sure you take a lot water with you and don't attempt to hike the whole length of Nahal Amud in one day.
The Hebrew guide (Shvil Israel by Yaacov Saar and Yagil Henkin / Eshkol publishing) שביל ישראל" יעקב סער ויגיל הנקין " has all the maps and hike description of the Yam le Yam route.