Autonomous colleges are colleges that are affiliated to some university (most colleges are affiliated to VTU) but form their own syllabus and conduct their own exam. The degree however is still awarded by VTU. Most other colleges follow the VTU syllabus and exam. Now as per the choice I think it's a personal choice. Autonomous colleges are often difficult to get into if you are rankings are average.

Placements after the degree largely depends on individual colleges and not on the way exams are conducted ( because everyone gets the same degree from VTU. Autonomous or Not)

So it's a personal choice.

Hope this clears your confusion.

Good luck!