It depends on your teachers, but there's little difference between the two AP exams. You can still get a 4 on the AP exam with 4/5/6 essays. I would recommend taking Lit unless you don't get any credit for your college(s) of choice.
In my opinion, you'll do better on the essays if you lengthily write about whatever the teacher believes to be true, then supporting that idea repeatedly with textual evidence. You don't have to believe in what you write, nor do you have to be interested in the passage/book. Ask your teacher what you can do to improve your essays, and just do them.
Here are two quotes on the supposed differences between Lang & Lit:
The literature exam tests a student’s ability to read and write about literature in English. It includes questions about poetry, drama, fiction, and nonfiction prose; the exam has one hour of multiple-choice questions and two hours of essay questions. |
The language exam tests a student’s ability to read and write about English prose and to write expository, analytical, and argumentative essays. Though a passage from a work of fiction can appear on the exam, the emphasis of the question or questions on the passage will be on language, style, and rhetoric. The exam has three 40-minute essays (two hours) and four sets of multiple-choice questions (one hour).
The principal academic activity in the AP English Language course is rhetorical criticism. In the AP English Literature course, it is literary criticism. For that reason, the primary texts for AP English Language are writings found in real-world communicative contexts, while the primary texts for AP English Literature come from the literary canon. Of course, these categories overlap. Literary works often have functional effects, and functional discourse often makes use of imaginative and artistic language. But in general, the works studied in an AP English Language course are nonfiction or the literature of fact. It should be a comfortable course for bright students who may not have a passion for literature but who can appreciate the power of language in a broad range of non-literary contexts.