You need to search, read and test. No one can give you an exact answer and threads asking for recommendations are against the posting rules, as they can cause bad feeling.
The kernel is the layer between the rom and hardware, it contains all the drivers etc to implement the software calls. Custom kernels will allow you change things that stock won't, usually with some risk.
Sent from my GT-I9300 using Tapatalk
Note: This quote doesn't automatically apply to everyone, decide for yourself if it might apply to you.
Originally Posted by justruss
What has this place become?
It's essentially a few people graciously answering the same repeating of immature, lazy, demanding questions from the masses.
Nobody searches. Nobody reads the first posts or titles of threads. Nobody even looks at posts a couple above their own.