Kernal BAdi vs Clasic BAdi

Hi Experts,

Below is my questions about kernel BAdi -

1.     What is kernel BAdi?

2.     Which BAdi is better form development perspective as well as business?

3.     Differences bw kernel BAdi and Classic BAdi.

Kindly provide the answers for above questions. It will really help me.

Thanks in advance,

Regards,
Arindam Samanta.