The only problem with LTSpice is it's learning curve, technically speaking it's as good as you get for a spice simulator. Pay software often adds simulation of a large variety of real world circuits and devices where LTSpice is a pure spice simulator. With LTSpice YOU have to define the entire circuit from scratch. Very very powerful but not for those week in math and technical knowledge. Spice will only simulate what you tell it to and can not mimic what will happen in a real world device. The simulated models for some pay software are more tuned to practical ciruit layout using standard components with known traits.