Hi,
Its better to complete CA articleship first and parallely clear all the exams of CS. This is because there is exemption from CS management training if you can show some practicle experience (min. 3 yrs.) in Job in a responsible position only in a company having paid-up share capital of not less than Rs. 25 Lacs. This experience you can easily show once getting into a job after qualifying CA. However it is true that you may not get the practicle expertise in corporate law and secretarial practice. Therefore, my advice to you would be to learn practicle aspects very hard during your articleship and study sincerely for CS. Knowledge will never go in vain.
Feel free to ask any further queries.