Not all Android stock ROMs have tweaks or Power Saving mode settings that come with your Android device. In addition, stock ROMs have bloatwares and applications from Google that are constantly active which consume not only battery but also resources. Changing from stock ROM to custom has many benefits and here's why CyanogenMod and Paranoid Android are famous for.

Stock ROM vs. Custom ROM
Stock ROM is a stable version released by the phone's manufacturer and rarely suffer from bugs but contains many bloatwares.

Custom ROMs are tweaked and contains little bloatwares but can suffer major bugs on early stages.

CyanogenMod
It is one of the most popular custom ROM you can find and free to download. Relatively, flashing CM to your device is very easy and packed with features such as CPU tweaking, battery management, RAM and ROM managers, CM apps, and more. Here are some reasons why you should choose CyanogenMod:

1. Performance Tweaks
You can get the clock speed of the device higher or lower affecting overall performance and battery life. Other tweaks include DSP manager for sound output, screen sensitivity, and UI animations without any third-party applications.

2. Apollo Music Player by CM
A personalised music player from CyanogenMod with the ability to set any song as ringtone, skip tracks using the lock screen interface, or long-press the volume keys.

3. Embedded into the system
Root access is very useful for CM ROMs which allows application to be embedded into the system rather acting as an individual program. This makes the device run solid, lightweight and consistent.

4. Very Snappy
Bloatwares make Android devices slow and most of these come with the stock ROM. CM ROMs have little bloatware and does not rely on background apps. This results on small-sized CM ROMs for as little as 87MB only.

5. AOSP Look and Feel
CyanogenMod may be customised, but it uses Android Holo-theme and appears like the vanilla version. The look is consistent, and applications will even adapt to the system theme.

Paranoid Android
Another custom ROM notable as well for being battery friendly. It is available to many different devices and CyanogenMod themes works with this ROM.

1. Overall Performance
Paranoid Android is very stable and highly customisable. Reviews suggest to use the ROM for a day or two to feel the tweaks and customisation before switching to another ROM.

2. Battery Life
Due to good stability of the ROM, Paranoid does not consume much in the power grid and many of its tweaks can help out save more juice. But be reminded, the user is main consumer of the battery. If you use the device heavily on games, Internet and video playback, you may actually need a power plant instead.

3. UI Smoothness
Fairly enough to match Android 4.2 Jelly Bean but not exceeding expectation, just the right smooth feeling.

4. Features
It is packed with features including UI for tablet or phone, Google applications, Paranoid settings and more.

RELATED STORIES