Hello dear student,

There are so many options for specializations that you can opt for after your bachelor's in computer science. But it only depends upon your interest there is nothing best if you are not interested in . May be one field is so good and you choose it as well but then you don't like it and you are not even getting interest in that . Then it will be complete waste of the time  and money . Few of the best specialised fields in cs are

Artificial intelligence

Cyber security

Computer graphics

Data processing

Software engineering etc

I hope this was helpful

Thank you