See depending on your interest you have to select the mode. For example if you want to pursue MSc Microbiology then firstly you will get very less university offering this course in correspondent and secondly this course will have no meaning if you do it in correspondence. The practical experimentation as well as a regularity of study is really very important for this kind of courses. Now if you want to shift your background like you want to study Management or Data Analysis etc then you can do it in online mode which will be much better than correspondence course. Companies like UpGrad etc gives really great offers for the online degree programs which can be a great way for you to learn the subject as well as you can utilize the knowledge by joining any industries.

So this are some of the perspectives which can be helpful to decide the mode.

I hope my answer helps. All the very best for your future endeavors!