The best colleges fir Btech are NITs and IITs and other government colleges. To get admission into then you need to qualify jee mains and advance. However there are many private universities too which can be a good option if you do not qualify in the entrance exam like Manipal, LPU, SRM, VIT, Galgotias etc.

Generally in most of the college you get admission based on your performance in their entrance exam not on the basis if your merit.

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Hope it helps.