There are many colleges offer three years law programme but Some of the top colleges you can prefer Faculty of Law Delhi University, Faculty of Law Banaras Hindu University, Punjab University, the colleges have its own entrance exam. The colleges have various societies like Moot court society, Legal Aid society, Debating Society etc where students can take part in various competitions/conferences/workshop and Legal aid camps which will help you to get the practical knowledge & good placement.

Here are some preparation tips you can follow the exam preparation:

Plan a strategy: It is a must to schedule a study-plan. An intensive preparation strategy is needed which includes as many as 6 hours of regular studies to crack DU LLB entrance exam. you must study at least two subjects every day and must practice at least one vocabulary / English and one reasoning exercise daily.
There is no defined syllabus for GK and current affairs in this exam. You can focus on important awards each year  sports, science, literature and arts, Physical geography, science and environment, Important happenings in the area of the Indian Constitution or Justice system
Mocks form an important part of the exam preparation. Look for a good online mock test series, and aim to write at least 6-8 mock tests before the actual exam. Reproduce the exam conditions as much as possible.

All the sectors are good & has value it depends on your interest & capability. Which other sector you are interested?

Good Luck!