Fibergl insulation vs. Blown insulation...which is best?

We live in upstate NY, and are remodling our hundred year old home. Which would be better for insulating the exterior walls. We would rather not take down exterior walls. The walls are sheetrocked over the plaster and lathe. During some remdloing we have noticed that there is blown insulation, but it has settled over the years. Would it be better to tear walls down and use standard insulation, or us the blown in. Also how is the blown in for retaining heat compared to fibergl? Cost is not a huge issue, as we can do this ourselves. Also, would adding a fiber board insulation sheeting to the interior walls beneath new sheetrock be effective? Thank you for your help.