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I have found Vision IAS is the best one for mains.

Enroll in its 20 or 25 full length mains exam test series. Here they will cover subject wise twice before going for full length.

Do not just give full length one that 8 test wala Series instead enroll for 20–25 tests series. This is subject wise and then full length.

Advantages:

1. It helps in covering the entire syllabus
2. It helps in revision
3. The questions are almost that of upsc standard: neither tough, nor easy. Almost similar
4. The best part is discussion where you learn a lot about answering questions.
5. If you are in OLD RAJENDR NAGAR then go and attend its discussion class. It's amazing
6. If you miss it then you can watch the video.

Though it has some drawbacks:

1. The evaluation in Vision IAS is not that good.
2. Here mostly aspirants check copy and the feedback is not that helpful.

Hacks:

1. You can download questions and answers from Xaam.in. This portal is very useful. xaam.in

There is an alternatives like Forum IAS mains guidance programme. It's mentoring system is good. You can ask your friends.

Whomever you find better you can go, enroll and start writing mains mock exam. Where ever you may enroll start giving mock exam honestly and seriously.