Our choice should be dictated by the passion for the subject you are taking as your optional, and the comfort level because in the long term those are the factors that help you keep going during times of adversity. If you intended to restrict yourself to coaching notes only, no syllabus is truly vast, authentic academic sources that the study material seems intimidating.
The preparation has to be done in four phases.
Phase - 1 : Focus on studying all the original source material and practising derivations for the first time. Making your own notes after referring to multiple books for the same topic. By the end of this phase, preferably by July or August, all your notes should be impeccably done and there should not be a need to go back to the source books except in special cases.
Phase - 2: The time for first revision and practising of problems.
Revision all topics one by one should be done.
Focus on clarity in writing and be innovative.
Meticulous descriptions as you would write in the exam hall.
Not give much attention in time yet.
This phase is for accuracy and innovation in answer writing.
Phase - 3: Focus should be on writing within the space permitted and the time allowed. Use rough notebooks to the fullest extent. Practicing and revising long derivations will improve your good answers writing skill. Writing through problems from past years CSE and IFoS papers within 3 hours timeline.
Phase - 4: Final Revision!
Make a short note, concise 20-30 page summary of your entire syllabus for revision on the way before the examination. In this phase, also note down intermediate positions of long derivations in the middle in some question in the exam.
Answer writing skills are very important, and is now more crucial than ever given that there is limited space to write answers. Choose you questions carefully and be sure about the 3 optional questions you can attempts from the 6 (besides the 2 compulsory questions). Though you cannot shuffle the questions around now, attempt them in an that you are comfortable in. This will boost up your confidence. Be very neat in your work and don't cross out or write illegibly. Presentation is paramount and a neat handwriting earns you the evaluator's good wishes automatically.
Draw a diagram. Any diagram even if its not essential, you should draw them. It put your paper in a different league and differentiates you from the rest. One must use two pens (blue and black) to bring out the contrast in the diagrams and they looked very distinctive on the answer sheet.
Innovation in writing answers: This is very tricky and a lot of work needs to go in for this to work out. For example, if a particular equations is derived, it would add value to the answer if you added a small insight on what the equation physically signifies. This is especially important in QM, Heat and Thermodynamics and Optics where equations often hide the physical significance of the phenomenon.
One must take the test series for Physics optional preparation from good institutes in New Delhi. A test series is invaluable in understanding how to write answer in very little time. Whether one should join classroom course as well is personal choice.