Both CBSE and ICSE are equally easy for a hard working student and both are difficult for a lazy lad.
It is very easy to score 10/10 in CBSE if you work hard and revise
But you need an extra hold over subject to cross 97% in ICSE

Opting for a CBSE school has its own share of pros, and the biggest advantage is that all major competitive examinations in India are based on the CBSE syllabus. These examinations include the Joint Entrance Examination (IIT-JEE), the All India Engineering Entrance Examination (AIEEE) and the All India Pre Medical Test (AIPMT)

The syllabus followed by the ICSE board is more comprehensive and complete, encompassing all fields with equal importance

ICSE is just a bit more difficult than CBSE.