It depends how you want to go about extending your battery life beyond what the OS does.
Greenify can be handy to put apps to sleep.
Juice Defender has a nice way of handling it (keeps network off, turns it on in intervals).
whoa...Avast has one but I never tried it...may take a look.
The question you need to answer is why aren't you getting the battery time you want? (too many background apps? weak cell signal?)
Do NOT use task killers; those will make your phone less responsive and use more power.