An app isn't going to save you battery life unless it controls your data sources (3G, WiFi, 4G) by turning them on and off. You can control your battery by tweaking the send/receive data schedules of your apps and leaving 3G, 4G, and WiFi off when you are not using those data sources. If you don't have your apps setup to send/receive data constantly you can leave WiFi on all day long and it wont drain the battery on your phone.
No need to use juice defender. I highly recommend investing in the 1750 mah battery from Seidio. Hence HTC is putting a 1730 mah battery into the EVO 3D.