Should I go for a LLB course or GDL course?

I have a degree in Business studies and a master’s degree in Social Science.
Should I apply for an LLB or a GDL?
Which one will be better and more efficient?
LLB: 3 years (full-time)
GDL: 9 months (full-time)
Is there any difference between the graduates of an LLB and a GDL in the context of a law firm?
Thanks.

The answer to your third question is no. Roughly half of the lawyers in many or most law firms will have degrees in law and the other half will have degrees in all sorts of thing and PGDLs. Anecdotally, it is suggested that the second most popular degree amongst lawyers is history, but PPE, economics, classics, modern languages, and STEM subjects also abound. Most lawyers practising hard IP law have STEM degrees.
The answer to your first and second questions is "it depends". If you are considering a legal academic career, or a career at the Commercial Chancery Bar, you might wish to take the time and spend the money to study law for two or three years as opposed to one year. Otherwise, you would qualify faster and a by taking a PGDL.
You could, by the way, do a "Senior Status" law degree in two years at a few universities, one of which is Cambridge.
Strictly speaking you can take the SQE without a PGDL, but it appears that law firms prefer applicants to have a PGDL if they do not have a law degree. The Bar requires that you have a law degree or a PGDL.