The trouble with such questions is usually finding people who have extensive experience with both products.

Anyone who's gained extensive experience in product 'A' will find product 'B' difficult to start with - simply because it's different.

As Russel says, both SDCC and Keil will get the job done - certainly at the beginner's level.

Keil, of course, would claim that the extra value comes in all the support for very many variants, including deviations from the "standard", and special features like banking (code & data) and extensive optimisations. None of which is likely to be of concern to a beginner.