@Thiyagarajan, it really depends on what you want to see.
If the answer is planets, you would have to buy a scope with a long focal ratio(f/8, f/9, f/10, for example). This makes it easy to magnify the planets so that you see it clearly. You also want to get something with enough aperture so that you get to see details on the planets. You will probably need a motorised mount so that the object stays in the field of view even at high magnifications.
If you want to do DSOs, you really need aperture. People usually use lesser magnification than needed for planets and hence you may not need a motorised mount to keep the object in the field of view. Dobsonians are very suitable for this as they give the most aperture for a given budget. You may find it difficult to do planetary observations with this as you will have to keep moving the scope to compensate for the earth’s rotation.
If you want to do astrophotography, a lot more factors come in. For planetary photography, you go for scopes with a long focal ratios and for DSOs you go for short focal ratios.