Custom ROM are provide a latest android version for android device.that update are not officially if you install it then your mobile warranty are void.so that are a risk and benefit.
1. CyanogenMod:
Custom Rom are provide unique feature and also add new feature that official android version are not provide.
Below show a top 5 Custom ROM provider.
1. CyanogenMod:
CyanogenMod is most popular custom rom in word that provide a latest version rom after few days.many of device are run on CyanogenMod ROM so that are amazing. this custom rom are support many of device.
site : cyanogenmod
2. AOKP:
This ROM are on many device word wild.AOKP has a feature that feature not get in your original stock rom.
3. Paranoid :
One best feature of paranoid is re-size of every app,widget,or system component with out change setting.
site : Paranoid
4. MIUI
In this Rom many of feature like virus scanner, data use ,back up ,lost device and theme customize.
site : MIUI
5. Liquid smooth :
liquid smooth best feature is here customize system.
site : Liquid smooth