Should I use reflective insulation over other kinds of attic insulation?
Something I didn't see mentioned is that along with proper insulation depth to get yourself to a minimum of R-36 also ensure your attic has proper ventilation. Attics need to breath to let hot air out in the summer and keep your roof cold during the winter (prevent ice dams). Windows have really bad R factors so if you only have single pane and cant get to double, consider storm windows. If your walls are "sweating" during the winter then they don't have enough insulation in them as well. For your wall ensure all your exterior gang boxes are sealed. A single can of foam spray can seal up almost all in a 2400 sq ft house.

As for the reflective insulation, it works well but only in hot climates as it acts a radiant barrier but there are numerous factors to ensure it works well. Doesn't do anything for cold.