We like Juice Defender. But I've not tried a lot of them. JD made a huge difference, so that was good enough for me.
But if you're using the phone a lot, playing games, away from wifi, etc, nothing is going to help much.
Samsung S4 (9505), Samsung S3, HTC Evo 4G LTE, HTC Evo 4G, HTC TouchPro 2, HTC 6700 (all Sprint)