Which option is better for COS of H4 to F1

Currently i am working in US and my wife is on H4 , i am planing to enroll in masters program and then eventually work on CPT or OPT after working COS to F1.

shall she come here on H4 and then go for F1 conversion or directly apply for COS from india for H4 to F1.

Which option would be ideal for safer and better process and how much time would it take for COS from H4 to F1.

I came to US on H1B in Feb 2018 and my VISA is till 11th September 2019. Any advice on this would be of great help.

Thanks & Regards,

Bharath